HER2-negative Patients Research Articles

Application of 21-gene recurrence risk score in patients with breast cancer

Objective: To investigate the relationship between 21-gene recurrence risk score (21-Gene RS) and the prognosis and clinicopathological features of hormone receptor (HR) positive, HER2-negative early breast cancer patients who did not receive neoadjuvant therapy. Methods: A total of 469 patients with HR positive and HER2-negative early breast cancer who received surgical treatment in the First Affiliated Hospital, Zhejiang University School of Medicine from January 2014 to October 2017 were selected. Their clinicopathological data were retrospectively analyzed. Tumor tissue samples were collected from patients, and the expression of 21-gene was detected by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR). The 21-Gene RS was calculated according to the Trial Assigning Individualized Options for Treatment (TAILORx) RS grouping and National Surgical Adjuvant Breast and Bowel Project B-20 (NSABP B-20) RS grouping principles. Patients were divided into low (21-Gene RS<11 or 21-Gene RS<18), intermediate (11≤21-Gene RS<26 or 18≤21-Gene RS<31) and high (21-Gene RS≥26 or 21-Gene RS≥31) risk groups, and the clinicopathological features and prognostic differences of patients in different risk groups were compared. Statistical data were compared by chi-square test. Survival analysis was performed using Kaplan-Meier curve analysis and the differences between groups were compared using Log-rank test. Multivariate analysis was conducted by COX regression analysis. Results: Based on TAILORx RS grouping, the proportions of low-risk, intermediate-risk and high-risk groups among the 469 patients were 18.8% (88/469), 48.2% (226/469) and 33.0% (155/469), respectively. Based on NSABP B-20 RS grouping, the proportion of low-risk, intermediate-risk and high-risk groups were 43.1% (202/469), 37.5% (176/469) and 19.4% (91/469), respectively. The association of 21-Gene RS with histological grading, luminal typing, Ki-67 expression, and chemotherapy and treatment modalities were statistically significant (P<0.05) regardless of TAILORx RS grouping or NSABP B-20 RS grouping. Kaplan-Meier survival curve suggested poor prognosis in high-risk group (P<0.05, Log-rank test). Multivariate COX regression analysis showed that surgical method and 21-Gene RS were risk factors affecting the prognosis of patients. Conclusions: 21-Gene RS is significantly associated with the prognosis of patients with HR-positive, HER2-negative, early-stage breast cancer not receiving neoadjuvant therapy, as well as with their clinicopathological characteristics such as patients' histologic grade, luminal typing, Ki-67 expression, and whether or not they are treated with chemotherapy or other treatment modalities.The 21-Gene RS threshold of 11 and 26 or 18 and 31 can be used to grade the prognosis in Chinese patients with early-stage breast cancer. More researches are needed to guide the selection of postoperative adjuvant therapy for patients with HR-positive and HER2-negative early-stage breast cancer.

Redefining anthracycline-related subclinical cardiotoxicity: 'Absolute' and 'relative' change in longitudinal strain.

Anthracycline chemotherapy (AC) for breast cancer can cause cancer therapy-related cardiac dysfunction (CTRCD) with resultant heart failure, traditionally defined as a reduction in left ventricular (LV) ejection fraction on echocardiography. In recent years, global longitudinal systolic strain (GLS) has been used to identify subclinical cardiac dysfunction prior to development of overt CTRCD. Recent harmonized guidelines have incorporated GLS into definitions for CTRCD to identify cardiac dysfunction and inform decisions regarding cardioprotective strategies. We evaluated subclinical dysfunction in breast cancer patients treated with AC and determined the echocardiographic and patient factors associated with significant GLS changes. One hundred fourteen HER2 negative patients treated with AC were prospectively recruited and underwent serial echocardiograms (LVEF and LVGLS) at three time points (prior to AC, 3months, and 1year). CTRCD was defined as an asymptomatic reduction in LVEF of 10% or symptomatic drop of 5% to LVEF <53%. Subclinical LV dysfunction was defined as a reduction of ≥10% in GLS compared with baseline, recognizing that this cut off identified an 'at risk cohort' rather than patients with established CTRCD. No participant demonstrated CTRCD by reduction in LVEF. Forty-three patients (38%) demonstrated a ≥10% relative reduction in GLS at 12months; 20/43 (47%) had a reduced absolute GLS to <16%, and were older, had hypertension, increased LV mass, lower baseline e' velocity and GLS. GLS ≥20.5% at baseline yielded a sensitivity of 79% and specificity of 87% for a normal GLS (i.e., ≥16%) at 1year despite a ≥10% reduction from baseline. We present a stepwise evaluation for subclinical LV dysfunction using both a relative reduction in GLS combined with an absolute reduction in GLS. We believe our findings may re-stratify patients with a high baseline GLS into a lower risk group despite transient relative GLS decrements ≥10%.

Breast cancer epigenetics: current and evolving treatment.

Breast cancer (BC) presents persistent challenges due to subtype-specific limited efficacy and potential resistance to standard therapy, influenced by the dynamic reversible nature of epigenetic plasticity. This study aims to comprehensively explore the evolving BC epigenetic landscape, analyzing trends and evaluating the therapeutic potential of epigenetic drugs (epi-drugs) for BC treatment. We conducted a cross-sectional study of BC epigenetic trials using ClinicalTrials.gov until July 18, 2023. Additionally, results from randomized controlled trials were retrieved from the registry or PubMed using trial registration numbers. In total, 22 epi-drugs were investigated in 100 trials, with 11 currently being studied in 38 ongoing trials for BC. Over the years, epigenetic clinical trials for BC have notably increased, with histone deacetylase inhibitors constituting 45.45% of the candidate agents in the development pipeline. All ongoing trials are enrolling human epidermal growth factor receptor2 (HER2)-negative BC patients. Epi-drugs are commonly explored in combination with multiple anti-cancer therapies, such as aromatase or microtubule inhibitors, using an intermittent sequential administration approach. Emerging strategies include new-generation epi-drugs and combination involving immunotherapy or targeted therapy. Among candidate drugs, tucidinostat and entinostat, in combination with exemestane, demonstrated significant improvements in progression-free survival in phase III trials for hormone receptor-positive, HER2-negative BC patients. This study highlights the growing interest in BC epigenetics, suggesting a potential shift from a one-size-fits-all approach to precision medicine, and emphasizes the necessity for robust evidence on their efficacy and safety to support continuous development and approval, addressing the unmet needs in BC treatment.

Evolution and prognostic significance of HER-2 changes from primary to residual disease in patients with HER-2–negative breast cancer receiving neoadjuvant chemotherapy.

583 Background: HER-2 changes during the neoadjuvant chemotherapy has not been thoroughly evaluated. The current study aimed to analyze the HER-2 status changes from primary to residual disease in HER-2 negative patients after neoadjuvant chemotherapy and evaluate its impact in survival outcomes. Methods: HER-2 negative breast cancer patients with residual disease after NACT who had paired pre- and post-therapeutic HER2 testing results were retrospectively analyzed. Data on clinical and pathological characteristics, treatment information, and survival outcomes were collected for all eligible patients. HER2 changes from the primary to residual disease were described and logistic regression were performed to identify factors associated with HER2 changes. The Kaplan–Meier method and multivariate Cox regression were used for survival analysis. Results: 571 HER-2 negative breast cancer patients with residual disease after NACT were enrolled, including HER2-zero (35.2%, n=201) and HER2-low (64.8%, n=370) patients before NAC. The overall rate of HER-2 changes rate was 32.4% (negative to positive 1.1%, low to zero 15.4%, zero to low 15.9%). Among the patients with HER-2-zero before NAC, patients with HER-2 changes (zero to low) were likely to be hormone receptor positive (68.1% vs 36.7%, P&lt;0.0001) and had a higher proportion of patients with Ki-67≤20 (Ki-67≤20 27.5% vs 15.6%, P=0.035). Among the patients with HER2-low before NAC, a higher proportion of hormone receptor negative were observed in HER2 changes patients (low to zero) (31.8% vs 18.4%, P=0.008) and the Ki-67 is relatively high in HER-2 changes patients (Ki-76 &gt; 20 73.9% vs 65.0% P=0.030). Multivariable logistic regression analyses showed patients with hormone receptor positive before NAC were related to underwent HER2-zero transferring to HER2-low (OR, 3.436, P&lt;0.0001). The median follow-up time was 50.0 months. In the HER-2 zero group, HER2 changes (zero to low) was significantly associated with better DFS comparing with constant HER2-zero (HR0.49, P=0.01) after adjustment, with 4-year DFS rate was 80.1%,55.7% (Log-rank P =0.033). Subgroup analysis showed that in the hormone receptor positive subgroup, patients with HER2 zero to low has a significant better DFS than patients with constant HER2-zero (Log-rank P=0.037). In the HER2-low group, no significant differences in survival outcomes between constant HER2-low and HER2 low to zero (HR1.07, P=0.778). Conclusions: HER2 status showed instability from primary tumor to residual disease after neoadjuvant treatment. HER2 changes (zero to low) was associated with better DFS in HER-2 zero patients.

Cisplatin monotherapy as a treatment option for patients with HER-2–negative breast cancer facing hepatic visceral crisis or impending visceral crisis: A single-center cohort study.

e13057 Background: The international consensus guidelines, ESO-ESMO's fifth edition, characterize visceral crisis (VC) in advanced breast cancer (ABC) as a swift rise in bilirubin during disease progression. The guidelines also briefly address the impending VC (IVC) definition. Systemic treatment data for hepatic VC/IVC are scarce and lacking in international guidelines regarding BC treatment. This study explores cisplatin monotherapy's safety and efficacy in HER2-negative BC patients with hepatic IVC/VC. Methods: In this retrospective cohort study conducted at a Reference Cancer Center in Southern Poland, data from HER2 negative ABC patients who underwent cisplatin monotherapy (60-80mg/m2, every 3-4 weeks) between 2016 and 2023 were examined. Hepatic VC followed ABC5 definition of rapid bilirubin elevation &gt;1.5 times the upper limit of normal (ULN) due to diffuse liver metastases, in the absence of biliary tract obstruction or Gilbert's syndrome; IVC was characterized by rapid, symptomatic liver progression, a majority of liver involvement, with ALT or AST &gt;2 x ULN, and significant increases in LDH, alkaline phosphatase, or GGTP. Results: The study included 33 female participants (24 hormonal positive) with a mean age of 53.8 years (range 34-77). Among them, 10 were identified with hepatic VC, and 23 with IVC. Median number of previous palliative systemic treatment lines was 2 (range: 0-5). The median progression-free survival was 1.87 months and the median overall survival was 2.67 months. Patients received median 1 cycle of cisplatin (1-6): 17 patients received only one cycle, 6 patients two cycles and 10 patients ≥three cycles. Using the Conditional Inference Trees algorithm allowed to assess that patients with performance status (PS) 0 or 1 (15 patients) had a 66.67% chance of achieving stable disease (SD) or partial regression (PR) as the best response, while patients with PS ≥2 (18 patients) had a 5.6% chance of achieving SD or PR as per Response Evaluation in Solid Tumors 1.1 Criteria (median time from cisplatin initiation to imaging studies 2.23 months). Eight patients experienced adverse events of grade ≥3, such as fatigue or nephrotoxicity leading to dose reduction in 5 cases and treatment discontinuation in 2. Conclusions: The differentiation between IVC and VC lacks precision. Due to the hepatotoxicity of BC-active drugs, specific recommendations for systemic treatment are lacking. Our study explored cisplatin's potential use, finding it to be a feasible choice in patients with PS ≤1 experiencing hepatic IVC/VC, regardless of liver function parameters. Almost one-third of our patients were administered treatment in the last 30 days of life, potentially adversely affecting their quality of life and causing unwarranted suffering and costs. Academic clinical trials should be organized to address this pressing medical gap.

Evaluating the efficacy of neoadjuvant endocrine therapy in HER2 low vs. HER2 negative breast cancer: An NCBD analysis.

599 Background: Neoadjuvant endocrine therapy (NET) is an important treatment option for hormone receptor (HR)-positive breast cancer (BC). Innovative ADCs targeting HER2 low tumors has sparked debate regarding the distinct nature of HER2 low tumors and whether it merits a unique treatment approach. With favorable outcomes in metastatic disease, there is interest in adopting similar strategies for early-stage treatment approaches. Methods: We examined the National Cancer Database for stage I-III ER-positive BC in women who underwent neoadjuvant endocrine therapy (NET) from 2010 to 2017, for at least 90 days to a maximum of 270 days. Patients with prior neoadjuvant chemotherapy, other malignancies, HER2-positive disease by either IHC or FISH, metastatic disease, or unknown stage were excluded. HER2 status was grouped as negative or low per 2023 ASCO-CAP guidelines. Patients’ response to therapy included pathologic complete response (CR), partial pathologic response (PR), stable pathologic response, or progression in primary tumor at time of resection. We employed multivariable binomial logistic regression to examine how clinicopathologic factors influence the probability of any response (combining CR and PR) to neoadjuvant hormonal therapy. Results: 3,808 patients met the inclusion criteria. 1,055 (27.8%) patients had HER2 negative disease, and 2,753 (72.2%) patients were HER2-low. 48 (1.2%) patients had primary tumor CR, and 1,484 (39%) had PR. Among HER2-low patients, 37 (1.3%) had pathologic CR, and 1,134 (41.1%) had PR. Among HER2-negative patients, 11 (1.0%) had pathologic CR, and 350 (33.1%) had PR. Multivariable logistic models revealed that age, duration of NET, and HER2 status were significant predictors of any response to NET. HER2-low tumors were more likely to have any response compared to HER2-negative (aOR=1.16, 95% CI 1.01 - 1.34, p=0.04). Patients who received &gt;150 days of hormonal therapy were more likely to respond (aOR=1.33, 95% CI 1.16 - 1.52, p=&lt;0.001); patients &gt;50 years old were more likely to have any response (aOR=1.41, 95% CI 1.07 - 1.90, p=0.02). Clinical node positivity and tumor grade did not have significant effect on response to NET at time of resection. Conclusions: Our study offers a real-world estimate of outcomes associated with NET in localized BC. HER2 low tumors had greater significant clinical responses to NET when compared to HER2 negative, suggesting that HER2 low tumors may benefit from tailored treatment in the neoadjuvant setting. [Table: see text]

Exploration of different immunogenomic TMEs in gastric cancer based on HER2 and PD-L1 expression.

e16073 Background: Recent results from the KEYNOTE-811 study showed that first-line pembrolizumab was superior to placebo with respect to progression-free survival (PFS) in combination with trastuzumab and chemotherapy in patients with HER2 positive metastatic gastric cancer (GC). Interestingly, In the subgroup analysis, the PFS benefit with pembrolizumab was significant in patients with tumors with PD-L1 CPS ≥1, whereas there was no benefit in the small subgroup of patients with tumors with CPS &lt; 1. Therefore, this study is to investigate immune-genomic differences in the tumor microenvironment according to the composition of surrounding cells and the expression status of HER2 and PD-L1. Methods: Utilizing single cell RNA sequencing (scRNA seq) and TCR sequencing, we examined 14 HER2 positive and 18 negative primary GC samples with CPS score based on PD-L1 IHC 22C3 pharmDx. Among the HER2-positive group, there were 4 samples in the CPS &lt; 1 (negative) and 10 samples in the CPS ≥1 (positive) group. In the HER2 negative group, there were 6 samples in the CPS &lt; 1 and 12 samples in the CPS ≥1. Results: First, when analyzing the distribution of total cells according to HER2 status, in the HER2 positive group, more endothelial cells ( p= 0.034) and fibroblasts ( p= 0.054) appeared in the PD-L1 negative group compared to the PD-L1 positive group, while there was no difference in the HER2 negative group. Furthermore, Through TCR analysis, the exhausted and cytotoxic score exhibit contrasting trends between HER2 negative and positive groups. In HER2-positive patients, the exhausted and cytotoxic score appear significantly higher in the CPS negative group. Next, we evaluated the proportion of immune cells according to HER2 status. The observed of CD4 Treg ( p= 0.084) and CD8 exhausted T (Tex), ( p= 0.036) cells was increased in the HER2 positive compared to the negative. When regrouped according to PD-L1 expression, only the HER2 positive group showed a tendency to increase the observation of CD4 Treg and CD8 Tex cells compared to positive in PD-L1 negative. In addition, we investigated whether the expression pattern of other immune checkpoint molecules differed depending on the PD-L1 expression pattern in both HER2 positive and negative patients. In the HER2 negative group, the expression of immune checkpoint proteins was similar regardless of the CPS expression group, or the expression of some proteins was higher in the CPS positive group. In other hands, in HER2 positive, CPS &lt; 1 group had higher expression of immune checkpoint proteins, such as PDCD1, LAG2, BTLA, VISTA and TIGHT. Conclusions: The high proportion of CD4 Tregs, CD8 Tex and the elevated exhausted score in the subgroup with CPS &lt; 1 in HER2 positive GCs suggesting immune exclusive environment compared to her-2 and PD-L1 coexpressing group. Considering increased expression of immune checkpoint proteins other than PD-1/PD-L1, for patients with HER2-positive and CPS &lt; 1, combination therapy with other immune checkpoint inhibitors rather than anti-PD-1/PD-L1 may be suggested.

A phase Ib/II study of an anti-CD137 agonist antibody ADG106 in combination with weekly paclitaxel and dose-dense doxorubicin/cyclophosphamide.

e14507 Background: ADG106 is a fully human agonistic anti-CD137 IgG4 monoclonal antibody which modulates the tumor microenvironment and has demonstrated increased efficacy when added to chemotherapy in preclinical models. We studied the combination of ADG106 with chemotherapy. Methods: We conducted a phase Ib trial in patients with advanced solid tumors to determine the recommended phase 2 dose (RP2D) of ADG106 + weekly P (paclitaxel 80mg/m2) or ddAC (doxorubicin 60mg/m2, cyclophosphamide 600mg/m2 Q2W with pegfilgrastim), followed by a phase II trial of neoadjuvant ADG106 + weekly Px12→ADG106 + ddACx4→surgery in stage I-III HER2 negative breast cancer patients. In phase Ib, one dose of single agent ADG106 was administered followed 2 weeks later by ADG106 + ddAC (Cohort 1) or ADG106 + weekly P (Cohort 2). Dose levels (DL) of ADG106 were 50mg (DL-1), 100mg (DL1), 200mg (DL2). Serial tumor biopsies were performed at baseline, after single agent ADG106 and at disease progression in phase I, and at baseline, after single agent ADG106, after cycle 1 ADG106 + P, and at surgery in phase II for translational studies. Results: 11 patients were enrolled into Phase Ib with median 3 (range 2-11) prior lines of palliative systemic therapy. ADG106 + ddAC (n=2 at DL1) was deemed intolerable with 1 patient experiencing G4 neutropenia and the other G3 infection; thus ADG106 was not added to ddAC in phase II. No DLTs were observed in all patients receiving ADG106 + P (n=6 at DL1; n=3 at DL2); ADG106 RP2D was declared at 200mg + P. In this cohort, the most common all-grade AEs were neutropenia (n=6), peripheral neuropathy (n=6) and fatigue (n=6); significant ≥G3 AEs were infection (n=2) and G3 neutropenia (n=6). 5/11 (45%) patients in phase I achieved clinical benefit (CBR; PR=2, SD=3) which is clinically meaningful as 9/11 (82%) had prior taxane exposure. 18 of the planned 30 patients have been enrolled into Phase II (ADG106+weekly P→ddACx4→surgery); 10 have completed study treatment and 5 have undergone surgery. While on ADG106 + P, 4 patients experienced G3 adverse events (AEs): neutropenia (n=3), hypophosphatemia (n=1), fever (n=1). Most common G1-2 AEs were ALT elevation (n=4), acneiform rash (n=3) and peripheral neuropathy (n=3). While on ddAC alone, all AEs were low grade except for 1 patient who had G3 pneumonitis from Pneumocystis Jiroveci Pneumonia. 26 sets of matched tumor biopsies have been collected (9 in phase I; 17 in phase II) and will be tested for a panel of 40 markers by multiplex IHC, including CD137, PD-L1, and CD3/4/8. Conclusions: ADG106 when combined with ddAC exacerbates neutropenia and is not tolerable despite prophylactic pegfilgrastim. The RP2D of ADG106 in combination with P is 200mg and is safe and tolerable; manageable G3 neutropenia was the most common AE. There are no new safety signals thus far in Phase II. Further efficacy analyses and studies on tumor immune markers are ongoing. Clinical trial information: NCT05275777 .

Use of Oncotype vs. Breast Cancer Index (BCI) for extended endocrine therapy decisions: A single center analysis in stage IA hormone receptor positive breast cancer.

e13083 Background: Extended Endocrine Therapy (EET) for hormone receptor positive HER-2 negative early-stage breast cancer reduces late recurrence risks but raises concerns about toxicity. Biomarker tests like the Breast Cancer Index (BCI) are vital for identifying patients who could benefit from continued ET, reassuring others against unnecessary extension. This study evaluates prognostic implications for both Oncotype Dx (Recurrence score, RS) and BCI amidst concerns about added testing costs in patients with early stage, estrogen receptor (ER) positive breast cancer. Methods: This is a single institution retrospective review of Stage IA ER positive HER-2 negative breast cancer patients who underwent both Oncotype Dx and BCI testing from January 2021 to December 2023. Pearson's correlation coefficient (r) was used to assess the linear relationship between the assays (p&lt;0.05 for significance), analysis was performed with SAS software, version 9.4. Results: Fifty-eight patients with Stage IA ER positive HER-2 negative breast cancer who had both Oncotype and BCI results were identified (100% female; mean age 72.2 years [54-87]). After a median followed up of 72 months (63-75), no systemic or locoregional recurrences were reported. A low positive correlation between Oncotype and BCI was observed across the entire cohort (r=0.4058; p=0.0016). However, subgroup analysis showed no significant correlations: Oncotype &lt;11 (n=17; r=0.2415; p=0.3504), Oncotype ≤18 (n=43; r=0.0914; p=0.5600), Oncotype &lt;26 (n=51; r=0.2530; p=0.0733); Oncotype ≥26 (n=7; r=-0.5634; p=0.1878). Correlation was also not found in patients with Grade 1 tumor (n=16; r=0.3138; p=0.2365). Thirty-nine patients (67.24%) had their treatment recommendation changed based on BCI results. Side effects from ET affected 15 patients (25.86%) and included arthralgias (60%, n=9), hot flashes (26.67%, n=4), depression (13.33%, n=2), insomnia (6.67%, n=1), and others (53.3%, n=8). Twenty-two patients (37.93%) developed new osteopenia, and 6 (10.34%) new osteoporosis while on EET. Eight patients (13.79%) had ET interruption during their treatment course. Conclusions: Despite inclination towards cost-saving measures, Oncotype DX may be more useful to give prognosis in the early adjuvant period whereas BCI is more useful to evaluate late recurrence risk. Low or high Oncotype scores and tumor grade may not align with BCI findings. Considering the importance of managing toxicity against the risk of late recurrence, incorporating BCI testing can enhance EET recommendations, even for Stage I, node-negative, ER positive patients.

Frequency of dose reductions of abemaciclib in metastatic and early-stage hormone positive, HER2 negative breast cancer.

e13099 Background: Abemaciclib is a CDK4/6 inhibitor which in combination with endocrine therapy (ET) improves progression-free survival in hormone receptor (HR)-positive, HER2 negative advanced breast cancer, as well as invasive disease free-survival in high-risk early-stage breast cancer. However, abemaciclib is associated with adverse events which may limit treatment adherence. In this single-center study, we describe real-world safety outcomes of early-stage and advanced HR-positive, HER2 negative breast cancer patients prescribed abemaciclib in conjunction with ET. Specifically, we analyze the frequency of adverse events and dose reductions (DR). Methods: We conducted a retrospective study of patients treated at Scripps Clinic between 1/1/2019-1/1/2023 with HR-positive, HER2 negative breast cancer prescribed abemaciclib with ET. Primary analyses were performed to discern clinical characteristic differences between groups. Categorical variables were summarized as frequencies and compared between arms by Chi-Square tests or Fisher’s Exact Tests. All continuous variables were summarized as means and standard deviations and compared between arms by T-Tests if normally distributed or summarized as medians and compared between arms by Mann-Whitney Tests otherwise. Statistical significance was set to 0.05 and all analyses were conducted in R. Results: A total of 77 patients were analyzed including 62% in the adjuvant setting and 38% in the metastatic setting. 51% of patients required DR. Patients requiring DR were older relative to those not requiring DR (59 vs 52 years of age, p=0.019). Those requiring DR remained on abemaciclib longer relative to those without DR (509 vs 350 days, p=0.057). Among those requiring DR, there were higher rates of grades II-IV diarrhea (p&lt;0.001) and Loperamide use (p=0.083). Those requiring DR also had higher rates of neutropenia (54% vs 29%, p=0.027), abdominal cramping (39% vs 8%, p=0.002), nausea (39% vs 13%, p=0.011), and fatigue (51% vs 32%, p=0.079). Among 9 patients who expired on abemaciclib, 7 were in the metastatic setting and 1 was linked to an adverse effect from abemaciclib; none required DR (24% vs 0%, p&lt;0.001). Finally, patients in the adjuvant setting remained on abemaciclib longer relative to those in the metastatic setting (526 vs 281 days, p=0.01). 95% of patients experienced symptom improvement with DR (p&lt;0.001). Conclusions: Our study describes real-world safety outcomes of patients with HR-positive, HER2 negative breast cancer treated with abemaciclib and ET. More than half of patients required DR. Those who reduced their abemaciclib dose had improvement of clinical symptoms and remained on therapy longer. Based on our findings and given the importance of adherence in treatment efficacy, a lower starting dose of abemaciclib may be a more tolerable strategy, especially among older patients who required more DR in our study.

The immunomodulatory impacts of endocrine therapy on host immunity in early-stage hormone receptor positive, HER2 negative breast cancer.

572 Background: Endocrine therapy (ET) reduces mortality in hormonally driven breast cancer (BC). The impacts of ET on the estrogen receptor are well known; however, there is limited data on the impact of ET on the host's immune system. This project aims to elucidate the potential immunomodulatory effects of ET-induced estrogen deprivation in HR+/HER2 negative early-stage breast cancer patients (pts) as well as baseline differences between BC pts and healthy controls (HC). Methods: Pts with Stage I-III HR+/HER2- BC initiating ET after completion of local regional therapy and/or chemotherapy were enrolled (NCT03719495). Whole blood, E1 (estrone) and E2 (estradiol) levels were collected at baseline (T1), 4 weeks (T2), 12 weeks (T3) and 24 weeks (T4) after ET initiation. 5 cohorts were enrolled: premenopausal and postmenopausal HCs, premenopausal pts on tamoxifen (TAM) or aromatase inhibitors (AIs) plus ovarian suppression, postmenopausal pts on AIs. Bulk RNA sequencing of whole blood was performed using NuGEN mRNA-seq on the Illumina Nova-seq platform. Differential expression analysis was performed using DESeq2 between HC and ET groups at T1, and between T1 and T4 within BC pts. The Benjamini-Hochberg method was used to adjust the P values for multiple comparisons. A curated set of 192 immune related gene signatures was used in the gene signature analysis. For each signature/module, a score was computed by taking the median of the expression values from all genes in each gene signature. CIBERSORT analysis was performed using the LM22 signature gene file and 100 permutations. Paired t-test was performed to compare T1 and T4. Results: Between 2019 and 2023, 64 pts were enrolled. Pts with missing samples or prior chemotherapy were excluded in this analysis. T1 samples of 25 pts with BC versus 14 HCs revealed marked changes in circulating immune cell (IC) composition with 537 DEGs (p value &lt; 0.05). Circulating ICs in BC pts had marked upregulation of genes associated with oxidative phosphorylation, adipogenesis, interferon alpha, reactive oxygen species compared to HCs. Immune cell composition was inferred by CIBERSORT analysis which suggests that BC pts had fewer circulating naïve B cells (p=0.048) whereas regulatory T cells (p=0.025) and activated NK cells (p=0.0039) were higher in BC pts than HCs at T1. BC pts with reductions in E1/E2 levels 6 months after ET had 77 DEGs in PBMCs between T1 and T4. Gene signature analysis shows that B cells and NK cells (p=0.0077) signatures are elevated post ET whereas a reduction of neutrophil signature (p=0.0034) was noted. Conclusions: There are significant differences in the baseline IC repertoire/activity in BC pts compared to HCs. The reduction in B cell activity/number and an increase in regulatory T cell number suggests a possible compromised immune system in BC pts. After surgery and 6 months of ET, these suppressed immune phenotypes reversed. Clinical trial information: NCT03719495 .

Personalized neoadjuvant strategy in ER positive and HER2 negative breast cancer to increase BCS rate (PLATO): A prospective, multicenter, phase II clinical trial.

595 Background: Neoadjuvant therapy significantly enhances the likelihood of breast-conserving surgery (BCS) in breast cancer patients. However, in ER-positive and HER-2 negative breast cancer, the response to neoadjuvant chemotherapy (NCT) is not as good as HER-2 positive or triple-negative breast cancer. In addition, with the evolution of multi-gene assays, many patients of this subtype may not require adjuvant chemotherapy. This study explores the potential of tailored neoadjuvant treatments (NCT or endocrine therapy (NET)) guided by 70-gene assay (Mammaprint, Agendia) to improve BCS rates in ER-positive/HER-2 negative breast cancer. Methods: A prospective, multicenter cohort study was conducted across four Korean centers from 2019 to 2023. Participants were clinical stage II-IIIA, ER-positive/HER2-negative breast cancer patients deemed unsuitable for BCS. Suitability was further verified by an independent three-surgeon panel using mammography or MRI. Out of 130 screened patients, 100 were enrolled. We analyzed 90 patients, excluding 10 cases; 2 with a basal type or HER2 type result in the blueprint, 7 who refused neoadjuvant therapy, and 1 who underwent surgery at another hospital. Before initiation of therapy, each surgeon recorded a target tumor size at which the surgeon would be able to do BCS considering location of the tumor and patient’s breast size. Based on the 70-gene assay results from core needle biopsies, high-genomic-risk patients received NCT (anthracycline + cyclophosphamide for 4 cycles, followed by 4 cycles of docetaxel), while low-risk patients underwent 16 weeks of NET with letrozole (±leuprolide for premenopausal women). Results: Out of the patients, 66 (73%) were high-genomic-risk and underwent NCT, while 24 (27%) received NET. Median tumor size was 3.7cm (85.6% clinical T2 and 14.4% T3/4). The primary endpoint, achieving the pre-established target tumor size for BCS, was reached by 70.0% (95% CI: 59.4-79.2%) of patients, significantly surpassing the set goal of 50.8% (a 15% increase from historical control). The rates were 74.2% for NCT and 58.3% for NET. The actual BCS rate was 58.9% overall (63.6% for NCT and 45.8% for NET). Clinically, 5.6% exhibited complete response (CR), 74.4% partial response (PR), 18.8% stable disease (SD), and 1.1% progressive disease (PD). Pathologic complete response (pCR) was achieved in 2.2% (all in the NCT group). No severe adverse events beyond expectations were observed. No pre-treatment clinical or pathological factor was significantly predictive for the BCS conversion. Conclusions: For ER positive, HER2 negative breast cancer patients initially ineligible for BCS, the use of pre-treatment multi-gene assays to guide selective NCT or NET could substantially increase BCS rates and reduce unnecessary chemotherapy. Clinical trial information: NCT03900637 .

Serial analysis of ESR1 and PIK3CA mutations in cell-free DNA from metastatic breast cancer during 1st line endocrine therapy.

e13060 Background: Activating mutations ofESR1 and PIK3CA genes are known mechanisms of endocrine resistance. Recent analysis supported benefit of early intervention at presence of ESR1 mutation in blood (bESR1) before clinical progression. We aimed to investigate ESR1 and PIK3CA mutations detected in cell-free DNA (cfDNA) from patients with hormone receptor-positive, HER2-negative metastatic breast cancer (MBC) and its impact on progression-free survival (PFS). Methods: Thirty patients undergoing 1st line endocrine therapy (ETx) were identified from a prospective cohort. Seven ESR1 hotspot mutations in the ligand binding domain were tested in cfDNA with droplet digital polymerase chain reaction (ddPCR) assay (Genopeaks Co., Ltd). Eleven PIK3CA hotspot mutations were tested using amplicon-targeted sequencing method (Genopeaks Co., Ltd) in both tumor and cfDNA. PFS analyses were performed using Kaplan-Meier methods and compared with the log-rank test. Results: We examined serial cfDNA samples from 26 patients collected every 3-6 months. ESR1 mutations were found in 61.5% (16/26) patients at any timepoint during 1st line endocrine therapy, with D538G being the most common followed by Y537C and 68.8% (11/16) being polyclonal. Among the 50.0% (8/16) bESR1 positive patients with clinical progression, 4 had bESR1 detected before clinical progression while 4 were diagnosed clinical progression concurrently, suggesting the necessity of closer intervals of cfDNA analyses. While presence of bESR1 did not affect PFS overall, 18.8% of patients with bESR1 detected within 6 months after 1st line ETx, displayed worse outcome (median PFS 5 vs 52 months). Also, patients with clearance of bESR1 mutation in subsequent cfDNA (81.3%, 13/16) were shown to have a better outcome (median PFS 52 vs 41 months). Among 14 patients with clinical progression, 8 had bESR1 mutation. Median PFS between patients with bESR1 positive vs negative was 14 vs 9 months. PIK3CA mutations were detected in 69.5% (16/23) of cfDNA at diagnosis of distant metastasis, among them 53.3% (8/15) had co-occurrence with bESR1 mutations. While presence of PIK3CA mutation in primary tumor tissue did not affect disease-free survival nor PFS, patients with blood PIK3CA mutation at diagnosis of metastasis displayed significantly worse outcome (p = 0.041). Conclusions: Substantial number of hormone receptor-positive, HER2-negative MBC patients were detected with ESR1 and PIK3CA mutation in plasma. Though it was a small-sized analysis to accurately assess statistical significance, we observed worse outcome in patients with 1) early detection (&lt;6 months) of bESR1 and with 2) sustained bESR1 during palliative ETx. Patients with clinical progression without bESR1 mutation displayed shorter PFS than patients with bESR1. PIK3CA mutations in cfDNA were prognostic supporting the benefit of combined targeted therapy.

Utidelone plus bevacizumab for the treatment of HER2-negative breast cancer brain metastases (U-BOMB): A multicenter, single-arm phase II study.

1081 Background: The primary treatment for brain metastases in patients with HER2-negative advanced breast cancer is predominantly local therapies like radiotherapy, owing to the limited efficacy of systemic therapies. Prior research has demonstrated utidelone's significant permeability across the blood-brain barrier and the preliminary effectiveness of bevacizumab for breast cancer brain metastases. Consequently, this study investigated the efficacy and safety of utidelone combined with bevacizumab in the treatment of advanced breast cancer brain metastases. Methods: This study was a single-arm, multi-center phase II clinical trial (NCT05357417). Eligible patients were aged 18 years or older with either radiotherapy-naive or progressive brain metastases post-radiotherapy, presented with asymptomatic or symptomatic brain metastases associated with HER2-negative breast cancer.Patients received intravenous bevacizumab (15 mg/kg on day 1 of each 3-week cycle) and utidelone (30 mg/m2 on days 1 to 5 of each cycle) until intolerance or disease progression. The primary endpoint was central nervous system objective response rate (CNS-ORR), as assessed according to the Response Evaluation Criteria In Solid Tumors version 1.1. Results: Between May 5, 2022, and October 25, 2023, a total of 46 patients were recruited, with a median age of 52.5 years (range, 33 to 69). Among them, 35 patients had untreated CNS lesions, while 11 had progressive brain metastases after local radiotherapy. The CNS-ORR was 43.5% (95% confidence interval [CI], 28.9%-58.9%). As of January 8, 2024, the median duration of follow-up was 14.6 months, and the median progression-free survival (PFS) was 7.7 months (95% CI: 5.5-10.8) as shown in Table. The 12-month overall survival (OS) rate reached 74.4% (95% CI: 60.0%-92.3%). The most common grade 1-2 adverse events (AEs) were peripheral neuropathy (87.5%), decreased neutrophil count (62.5%), anemia (47.5%), diarrhea (37.5%), and increased alanine aminotransferase (25%). No grade 3 or higher treatment-related AEs occurred. Conclusions: This study preliminarily shows promising efficacy and manageable safety of the combination of utidelone and bevacizumab in the treatment of HER2-negative metastatic breast cancer patients with brain metastases. Clinical trial information: NCT05357417 . [Table: see text]

Results and exploratory biomarker analyses of a phase II study CHANGEABLE: Combination of HX008 and niraparib in germ-line-mutated metastatic breast cancer.

1084 Background: The combination of poly (ADP-ribose) polymerase inhibitors and immune-checkpoint inhibitors demonstrated synergistic antitumor activity in preclinical studies. Here we report the efficacy, safety, and biomarker analyses of the combination of niraparib and PD-1 inhibitor HX008 in metastatic breast cancer (MBC) patients with germline DDR gene mutations in a phase II trial (CHANGEABLE). Methods: Eligible patients had histologically confirmed MBC with at least one measurable disease and germline pathogenic/suspected pathogenic mutations in DDR genes. Patients were enrolled into two cohorts: the main cohort (HER2-negative MBC patients with gBRCA1/2, gPALB2, gCHEK2) and the exploration cohort (MBC patients with gDDR gene mutations and brain metastases). Simon's Two-Stage design was used for recruiting patients in the main cohort. Patients with HER2-negative MBC received niraparib 200 mg qd combined with HX008 200 mg q3w, while HER2-positive patients received additional anti-HER2 TKI pyrotinib 400mg qd if having brain metastases, until disease progression. The primary endpoint was ORR. NGS of tissue and ctDNA were performed for exploratory biomarker analyses. Results: As of January 12, 2024, 37 patients were enrolled. In the main cohort with gBRCA1/2 mutations (n = 28), ORR was 78.6% (22/28), with 3 patients having complete response. DCR was 96.4% (27/28). Median PFS was 7.3 months (95%CI 4.2 to 10.4). According to Simon's Two-Stage design, since two patients with gCHEK2 mutations in the first stage had only stable disease, the recruitment was terminated. One patient with gPALB2 mutation had stable disease and the remaining one is in the screening process. In the patients having brain metastases (exploration cohort), ORR was 40% (2/5) and DCR was 80% (4/5). The most common treatment-related adverse events of grade 3 or higher were anemia (13 [35.1%]), thrombocytopenia (4 [10.8%]), and neutropenia (3 [8.1%]). No treatment-related deaths were reported. In the biomarker analysis, NGS of 700 genes was performed on 24 patients with gBRCA1/2 mutations in the main cohort. No significant difference was found in ORR or PFS between gBRCA1 and gBRCA2 mutations. Somatic mutations in XPO1 (16 patients (73%), 15/18 PR+CR, 1/4 SD+PD) showed significant correlation with response. Somatic TP53 mutations are significantly correlated with shorter PFS, while ASXL1 mutations are significantly correlated with longer PFS. Four somatic mutations (AR_c.1418_1420del, AR_c.231_239dup, 2 DUSP22 mutations) showed a consistent trend of decreasing in PD samples, while NF1_c.3198-4dup showed a consistent trend of increasing in PD samples. Conclusions: The combination of niraparib and HX008 demonstrated promising clinical benefits with a tolerable safety profile in MBC patients with germline BRCA1/2 mutations, even in patients with brain metastases. Clinical trial information: NCT04508803 .

Exosome-delivered microRNAs confer adriamycin-resistance through modulating the immune and metabolism-related gene PTEN in HER2-negative breast cancer.

e12500 Background: Anthracycline is widely used in breast cancer (BCa) chemotherapy, but acquired drug resistance remains a challenge. Increasing evidence suggests that changes in the tumour immune microenvironment (TIME) consistently contribute to the development of chemoresistance. Methods: TIME scores and tumor-infiltrating immune cells (TICs) scores were used to investigate the prognosis, characteristics and gene transcriptomic profiling of HER2-negative BCa patients who received anthracycline chemotherapy. Exosomes from MCF/7-ADR (ADR-exos) and MCF/7-S cell lines were characterized. Dysregulated miRNAs were obtained by using miRNA microarray analysis on BCa cells and their corresponding exosomes. Protein profiling was performed to identify differentially expressed proteins in up- and down-regulated miR-222 cells. Ability of ADR-exos to transfer drug-resistance mediated by miR-222 was assessed by immunofluorescence assay and flow cytometry. Conditions to load miR-222 mimic or inhibitor into exosomes were optimized. Influence of miR-222 inhibitor-containing exosomes on the downstream pathway of miR-222 and the potential therapeutic effects were evaluated. Relationship between miR-222/PTEN and drug resistance in circulating exosomes from mice after doxorubicin chemotherapy was investigated. Results: Firstly, we discovered the complicated and heterogeneous TICs subtypes and their unique biological behaviors in HER2-negative BCa. Then, we identified 85 differentially expressed immunologic signature gene sets and 7202 corresponding immune-related genes in three subtypes quantified by gene set variation analysis. We identified 12 up-regulated and 13 down-regulated genes using miRNA microarray analysis in doxorubicin-resistant cells and their exosomes. Mass spectrometry found 45 differentially expressed proteins affected by miR-222. Moreover, we successfully established miRNA mimic/inhibitor-containing exosomes to explore the solo function of exosomal miR-222 in doxorubicin-resistance both in vitro and in vivo. For the first time, we detected the levels of miR-222 and its target gene PTEN in circulating exosomes from mice after doxorubicin-based chemotherapy and explored the potential clinical implications of miR-222/PTEN-containing exosomes in chemotherapy and immune suppression of BCa. Conclusions: Doxorubicin-resistant cells can transmit drug-resistance to sensitive cells via delivering miR-222 by modulating the immune- and metabolism-related gene PTEN without interference from other relevant drug-resistance factors in exosomes. Therefore, miR-222-containing exosomes and their target gene PTEN may be a promising biomarker for predicting chemotherapy efficacy and tumor immunity regulation in BCa patients receiving anthracycline chemotherapy.

Neoadjuvant dalpiciclib, exemestane, and goserelin in premenopausal women with HR-positive, HER2-negative breast cancer: A prospective, multicenter, randomized two-group, non-controlled phase 2 clinical trial.

TPS625 Background: The combination of CDK4/6 inhibitors (CDK4/6i) with endocrine therapy has significantly improved progression-free survival and overall survival in patients with HR-positive, HER2-negative advanced breast cancer (BC), revolutionizing the treatment landscape. However, previous CDK4/6i neoadjuvant studies have predominantly focused on postmenopausal populations, leaving a gap in preoperative treatment for early HR-positive, HER2-negative premenopausal BC patients. Therefore, the present trial is conducted to investigate the efficacy of dalpiciclib, exemestane and goserelin as neoadjuvant therapy in premenopausal women with HR-positive, HER2-negative BC. Methods: This is a multicenter, randomized two-group, non-controlled phase 2 clinical trial. Key eligibility criteria include: Patients aged 18 years or older with no prior treatment, an ECOG performance status of 0-1, at least 1 measurable lesion, and clinical stage II-III HR-positive, HER2-negative premenopausal invasive BC. Initially, all enrolled patients will receive two cycles of treatment with docetaxel, doxorubicin, and cyclophosphamide (TAC). Subsequently, patients with complete response (CR) or partial response (PR) will receive an additional four cycles of TAC, whereas patients with progressive disease (PD) will undergo surgery or treatment options decided upon by the investigators. Those with stable disease (SD) will be randomly assigned 1:1 to either an experimental group receiving 16 weeks of dalpiciclib, exemestane, and goserelin (dalpiciclib: 125 mg daily for 21 days followed by 7 days off, exemestane: 25 mg daily for 28 days, goserelin: 3.6 mg every 28 days) or a standard chemotherapy group receiving four more cycles of TAC. Treatment response is assessed according to RECIST 1.1 criteria. Surgery will be performed after completion of the planned neoadjuvant treatment, followed by radiation therapy and systemic treatment according to local guidelines or the investigators' choices. The study's primary endpoint is the objective response rate (ORR) of the experimental group. Secondary endpoints include the ORR, residual cancer burden, preoperative endocrine prognostic index, event-free survival, and safety of both. Using Simon's two-stage optimal design and assuming a 40% response rate as desirable in the experimental group, at least 13 responses among a total of 43 patients were required to meet the primary endpoint. The trial will be terminated if fewer than 3 patients respond in the first stage. Considering an 80% SD rate post two neoadjuvant TAC cycles and a 10% attrition, the sample size was ultimately set at 119. The trial is actively recruiting. Clinical trial information: NCT06009627 .

Safety and efficacy of intensified preoperative management of locally advanced gastrorsophageal junction cancer (INPROVE).

e16110 Background: The optimal management of locally advanced gastroesophageal junction adenocarcinoma (LAGEJad) is not fully established yet. Both neoadjuvant chemoradiotherapy (CRT) and perioperative taxane-based triplet chemotherapy (CT) are acknowledged treatment options for Siewert I and II cancers. In this retrospective study, we aimed to assess the safety and outcomes of an intensified preoperative regimen combining taxane-based triplet CT and CRT. Methods: We conducted a retrospective analysis of a cohort comprising 16 consecutive HER2 negative patients (pts) with LAGEJad treated at the Centro di Riferimento Oncologico of Aviano between 2019 and 2022. All pts received induction CT (iCT) consisting of fluoropyrimidine, oxaliplatin and docetaxel, followed by CRT (45Gy/25Fr) with simultaneous boost and concomitant CT. Surgery (Ivor-Lewis or McKeown) was performed 8 weeks post-CRT. Clinico-pathological (CP) and treatment features were analyzed using logistic regression to assess their association with response to iCT-CRT. The association of iCT-CRT with survival outcomes was investigated using the Kaplan-Meier method. Results: Key CP data are summarized in Table 1. Median age was 59 years, all pts were male. At diagnosis, 81.2% of pts exhibited cT3+ and cN+ disease. All pts received iCT and CRT. The rate of partial responses was 50% after iCT and 68.8% after CRT. Overall, 12 pts underwent surgery, all achieving R0 resections within a median timeframe of 9 [8.5;11] weeks post-CRT. Among them, 25% had a pathologic complete response, while 62.5% attained a Mandard tumor regression grade (TRG) of 1-2. No new safety signals emerged from iCT (only 2 pts had ≥G3 diarrhea) or CRT (≥G3 mucositis occurred in 6.2% and anemia in 6.2% of pts). No significant surgical delays were observed, although 5 pts experienced post-operative complications (4 grade I, 1 grade IIa). There were no statistically significant associations between CP variables and response to the iCT-CRT. Relapses were seen in 8 pts (2 locoregionally); 3-year survival was 46%. Median event-free survival was 5 [5;11] months, while median overall survival 34 [14;NR] months. Conclusions: The intensification of preoperative treatment in pts with LAGEJad is active and safe: the surgical schedule was not significantly delayed, and the safety profile remained comparable to standard regimens, with no major complications reported. Randomized clinical trials are ongoing to assess the clinical benefits of this approach. [Table: see text]

Abstract PO5-14-02: Diagnostic leukapheresis to increase CTC detection rate in breast cancer patients after 5 years of adjuvant endocrine treatment

Abstract Purpose: Patients with early hormone receptor positive, HER2 negative breast cancer have a risk of recurrence for up to 20 years after the initial diagnosis and is therefore treated with adjuvant endocrine treatment (ET) for 5 to 10 years. As a result there is a large proportion of patients that overtreated, hence, an urgent need for better biomarkers to guide treatment decisions. In previous research, it was shown that circulating tumor cells (CTCs) are detected in 5% of patient after 5 years of adjuvant treatment and that this indicated a 13-fold higher risk of recurrence, with a median lead time of 2.8 years. However, the sensitivity and specificity of the test were moderate. This could be caused by stochastic variation, given the low numbers of CTCs detected in 7.5 ml peripheral blood. We hypothesized that increasing the screening volume, increases the test statistics. Methods: In this study, we investigated whether increasing the screening volume by diagnostic leukapheresis (DLA) can increase the detection rate of CTCs (CellSearch platform). With DLA, 5 liters of peripheral blood was screened, which in previous studies had shown to increase the CTC-yield per ml by 25-fold. To this end, we included early hormone receptor positive, HER2 negative breast cancer patients that were treated with ET for 4.5-5.5 years with no signs of disease recurrence. We compared the number of detected CTCs in the standard fraction of 7,5 mL peripheral blood (PB), to buffy coat (30 ml), to DLA sample (200 × 109 white blood cells (WBC), equal to 25-50 mL PB) and to DLA after WBC depletion. Results: Thirty two hormone receptor positive/HER2 negative breast cancer patients were included in this study after a median duration of ET of 60 months, of which 3 (9%) patients completed ET according to clinical guidelines and the remaining patients were still on treatment. Twenty eight patients (88%) had 1-3 positive lymph nodes at diagnosis, and 3 patients had 4-9 positive lymph nodes. The Clinical Treatment Score at 5 years (CTS5 score) was intermediate or high in 75%, and unknown in 19%, indicating a recurrence risk of &amp;gt;5% at years 5-10 after diagnosis. In none of the included patients, CTCs were detected in 7,5 ml PB, nor in any of the other tested blood volumes. To date, 2 patients have been diagnosed with overt metastatic disease during follow-up. DLA was well tolerated and did not cause adverse events. Conclusions: We conclude that DLA was unable to increase the detection rate of CTCs in hormone receptor positive, HER2 negative patients with early breast cancer being on treatment for a median duration of 5 years. Additional circulating tumor DNA analyses are planned. Citation Format: Noortje Verschoor, Jaco Kraan, Johanna Zuetenhorst, Mijntje Vastbinder, Jan Drooger, Stefan Sleijfer, Saskia M Wilting, John WM Martens, Agnes Jager. Diagnostic leukapheresis to increase CTC detection rate in breast cancer patients after 5 years of adjuvant endocrine treatment [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-14-02.

Abstract PO3-16-02: Trastuzumab and taxane chemotherapy in the first-line in MBC patients with a HER2-negative primary tumor and HER2-positive circulating tumor cells: a phase II trial

Abstract Purpose: HER2 overexpressing circulating tumor cells (CTCs) are observed in up to 20% of HER2-negative metastatic breast cancer patients. Since targeted anti-HER2 therapy has drastically increased the outcome of patients with HER2 positive breast cancer, we hypothesized that patients with HER2 overexpressing CTCs might benefit from the addition of trastuzumab to chemotherapy. Methods: In this single-arm, phase II trial, HER2 negative patients with HER2-positive CTCs received trastuzumab as addition to first-line treatment with taxane chemotherapy (trastuzumab group). Patients with detectable CTCs but without HER2 overexpression and that received taxane chemotherapy only, were used as internal control group (taxane monotherapy group). The primary outcome measure was progression-free rate at 6 months (PFR6). The study was powered to reach a PFR6 of 80%; in this case this strategy was considered worth further investigation. In November 2022, the study was terminated early due to slow patient accrual. Results: 63 HER2 negative patients with metastatic disease were screened, of which 8 patients had HER2-positive CTCs and were treated in the first line with trastuzumab in addition a taxane. Patients receiving taxane monotherapy were used as a control group (n = 27). The median number of CTCs was 15 (range 1 – 131) in patients with HER2-positive CTCs, compared to median 5 (range 1-1047) in the control group. PFR6 was 50% in the trastuzumab group and 64% in the taxane monotherapy group, with no significant difference in median PFS (8 versus 9 months, p=0.51). Excluding the patients that had no measurable CTCs, there was a borderline significant difference between median CTC count in the patients that did and that did not have HER2 positive CTCs (p=0.05). We confirmed a significant higher CTC-count in samples that had at least one HER2-postive CTC in an independent patient set (n=233, p&amp;lt; 0.001). Conclusions: Although this study was performed in a limited number of patients, no clinical benefit of trastuzumab was observed. Firstly, we conclude that our strategy was not feasible for clinical implementation due to high numbers needed to screen. And, second, due to the strong correlation between CTC numbers and detected CTC HER2 positivity, the prognostic value of the CTC numbers precludes judgement of any predictive value of the HER2 status of CTCs. Citation Format: Noortje Verschoor, Manouk Bos, Inge de Kruijff, Ngoc M Van, Jaco Kraan, Jan Drooger, Johanna Zuetenhorst, Saskia M Wilting, Stefan Sleijfer, Agnes Jager, John WM Martens. Trastuzumab and taxane chemotherapy in the first-line in MBC patients with a HER2-negative primary tumor and HER2-positive circulating tumor cells: a phase II trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-16-02.