Chemotherapy For Metastatic Breast Cancer Research Articles

HOPE: Harnessing olaparib, palbociclib, and endocrine therapy for BRCA1/2-associated HR+, HER2- metastatic breast cancer.

10616 Background: Thepoly (ADP-ribose) polymerase inhibitor olaparib yields superior progression-free survival, response rates and patient-reported outcomes compared with chemotherapy in patients with BRCA1- or BRCA2- ( BRCA1/2) associated metastatic breast cancer (MBC). Fulvestrant and palbociclib improve outcomes in patients with hormone receptor-positive (HR+) MBC. HOPE (NCT03685331) is a phase I trial to evaluate combination olaparib (O), fulvestrant (F), and palbociclib (P) in patients with BRCA1/2-associated HR+, HER2 negative MBC. Methods: A 3+3 dose escalation was used to assess safety and preliminary efficacy of O, F and P. Eligible participants (pts) had HR+ MBC, a germline (g) or somatic (s) mutation in BRCA1/2, measurable/evaluable disease, any/no prior endocrine therapy, and 0-2 prior lines of chemotherapy for MBC. Prior PARPi and CDK4/6i were permitted but not in combination. Palbociclib was added after a 28-day safety run-in (Cycle 0) of O + F alone. Fulvestrant dose was 500mg IM on day 1 of each 28-day cycle. Dose level 0 (DL0, starting level) was F, O 300mg orally BID continuously, P 75mg orally daily on days 1-21; DL-1 was F, O 250mg orally BID, P 75mg orally daily on days 1-21. The primary endpoint was MTD (adverse events (AEs) based on CTCAE v5.0). Dose limiting toxicity (DLT) period included Cycles 0 and 1. A 30% DLT rate was acceptable; 6 pts had to be treated at a dose for it to be declared MTD. RECIST v1.1 was used to evaluate response. Results: Eight treated pts (s BRCA1:1 ;g BRCA2:6; s BRCA2:1 ) had median (M) age 47; M 0 (0-2) prior lines of endocrine therapy and 0 (0-1) prior chemotherapies for MBC. Three pts each had received O, F, and CDK4/6i as part of their standard of care treatment before study. At DL0, 2/2 pts had DLT with persistent grade(G) 3 neutropenia. Among 6 pts treated at DL-1, none experienced DLT, but 3 pts missed doses of study treatment due to cytopenias (G3 neutropenia, G3 leukopenia, G3 thrombocytopenia) during the DLT period. Following the DLT period, 1 pt reduced O to 200mg orally daily and 1 discontinued P based on provider discretion due to cytopenias (G3 neutropenia, G3 thrombocytopenia). Grade 3 AEs occurring in >1 pt related to study treatment were: neutrophil count decrease (G3/2, n=5/2); white blood cell decrease (G3/2/1, n=3/2/2); platelet count decrease (G3/2/1, n=2/0/1). Overall related AEs in >50% of pts were anemia (n=7), fatigue (n=6) and nausea (n=5). Best responses were CR/PR/SD/PD in 1/1/5/1 pts. Conclusions: MTDof O, F and P (DL-1) was reached and demonstrated antitumor activity. Although no AEs meeting protocol-specified DLT criteria were observed at MTD, hematologic toxicity at this dose complicated drug delivery and required close monitoring during and after the DLT period. Combinations utilizing PARP1 selective inhibitors, lower doses of therapy or sequential rather than combination therapy may improve feasibility. Clinical trial information: NCT03685331 .

Abstract PO5-05-03: Phase 1/2 Dose Expansion Study Evaluating First-In-Class eIF4A Inhibitor Zotatifin in Patients with ER+ Metastatic Breast Cancer

Abstract Background Zotatifin (eFT226) is a first-in-class, potent and sequence selective inhibitor of RNA helicase eIF4A that promotes a stable mRNA:eIF4A:drug ternary complex at specific polypurine motifs present within the 5’-UTR of select transcripts, thereby blocking production of the encoded proteins. In preclinical models zotatifin treatment simultaneously down-regulated translation of numerous oncogenes including CDK4, ERα, ERBB2, KRAS, and CCND1. Previous clinical research has demonstrated the activity of zotatifin in combination with other agents in ER+ metastatic breast cancer (MBC). Methods Part 1 is a 3+3 dose escalation portion of the protocol followed by Part 2 as a Simon’s two-stage design in patients with ER+ MBC enrolled at the recommended phase 2 dose (RP2D) of zotatifin (0.07 mg/kg IV two weeks on/one week off) in combination with fulvestrant (ful) and abemaciclib (abema) (Z+F+A). Part 1a and Part 1b are 3+3 dose escalation portions evaluating zotatifin in combination with ful (Z+F) at QW IV and Q2W IV dosing schedules, respectively. Key eligibility criteria included at least one line of therapy for advanced/metastatic disease, progression on hormone therapy, and in addition, the Z+F cohorts required prior CDK 4/6 inhibitor (CDKi). Primary endpoint of Part 1a/1b was determination of RP2D and primary endpoint of part 2 was objective response rate (ORR) per RECIST v1.1. Additional endpoints included safety, progression-free survival (PFS) and other efficacy analyses, and characterization of pharmacodynamic (PD) markers and pharmacokinetics. Results As of a data cut-off of July 6, 2023, 20 pts were enrolled in the Z+F+A cohort and had a median of four prior metastatic lines of therapy. In 19 evaluable pts in Z+F+A cohort, there were four confirmed partial responses (PR), one unconfirmed PR, and 10 pts with best overall response (OR) of stable disease (SD). All pts with PR/unconfirmed PR received prior CDKI, ful, and chemotherapy for MBC. Confirmed PRs were observed in patients with and without mutations in ESR1 and PIK3CA. mPFS, while not yet mature, exceeds 20 weeks. In Z+F+A the most common adverse events (AEs) were diarrhea (80%, all grades (Gr)) and nausea (75%, all Gr 1/2) and the most common Gr 3/4 AE was diarrhea (15%). In Z+F cohorts of 0.07 mg/kg QW (n=3), 0.1 mg/kg Q2W (n=3), and 0.14 Q2W (n= 2) there were no dose-limiting toxicities or Gr 5 adverse events (AEs). There was one confirmed PR and one SD in 0.1 and 0.14 mg/kg Q2W cohorts, respectively, and no PR or SD in the 0.07 mg/kg QW cohort. In Z+F+A, 9 pts had paired pre- and on-treatment ctDNA analyzed by Guardant assay. Of the remaining 11 pts, 4 came off study prior to scheduled collection of the on-treatment sample and 5 had unavailable samples. Of the 9 patients with paired samples, 8 had ctDNA decreases of >50%, all of whom had SD or PR. In the Z+F Q2W cohort, 2 of 3 patients had ctDNA decreases >50%, one of whom had a PR. Reduction below the limit of detection was seen for mutant alleles in ESR1, PIK3CA and other genes with potential to confer resistance to endocrine therapy. Conclusion Z+F+A showed encouraging efficacy in heavily pretreated ER+ MBC patients, with results that compare favorably to other treatment options available after progression on CDKi plus endocrine treatment. Efficacy was seen independent of ESR1 or PIK3CA mutations, suggesting the potential to treat a broad, unrestricted patient population. Initial results with Z+F Q2W dosing are encouraging and support continued dose escalation of this regimen. Citation Format: Ezra Y. Rosen, Manish Sharma, David Berz, Jennifer Caswell-Jin, Georgina Fulgar, Mark Densel, Gary Chiang, Samuel Sperry, Douglas Warner, Funda Meric-Bernstam. Phase 1/2 Dose Expansion Study Evaluating First-In-Class eIF4A Inhibitor Zotatifin in Patients with ER+ Metastatic Breast Cancer [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 PO5-05-03.

Abstract PO5-01-01: The comparison of HER2 low and HER2 0 in ductal carcinoma in situ (DCIS) for breast cancer

Abstract Background: Trastuzumab deruxtecan is a standard of care after prior chemotherapy for metastatic breast cancer with HER2 low. HER2 low recognized as a new category of breast cancer. The definition of HER2 low is IHC 1+ or IHC 2+/ISH- in invasive ductal components. We have already reported the frequency and prognosis of HER2 positive and low in invasive cancer (Breast Cancer. 2022;29:234-241), but the distribution and characteristics of HER2 low in ductal carcinoma in situ (DCIS) is unknown. It is also well known that HER2 expression is higher in DCIS than in invasive cancer. We focused on the frequency of HER2 low in DCIS, performed an analysis of its frequency and characteristics, and compared to DCIS with HER2 0. Methods: We retrospectively examined breast cancer patients with DCIS and invasive ductal carcinoma (IDC) who underwent surgery at our institution between 2005 and 2015. Regarding the expression status of HER2, we classified cases into three groups: HER2 0, HER2-low (defined as IHC 1+ or IHC 2+/ISH-), and HER2-positive (IHC 2+/ISH+ or IHC 3+), and investigated their frequency. We analyzed the relationship between HER2 expression and Van Nuys classification, as well as the relationship between HER2 expression and ER expression, using the chi-square test. Results: A total of 726 DCIS patients were included in this analysis. The patient demographics showed a median age of 52 years (range: 20-84), with 413 patients (56.9%) undergoing total mastectomy and 311 patients (42.8%) undergoing breast-conserving surgery (two cases had unknown surgical procedures). The expression of HER2 in DCIS patients was observed as HER2-0, low and positive in 100 (13.8%), 474 (65.3%) and 152 patients (20.9%), respectively. The expression of HER2 in IDC was observed as HER2 0, low and positive in 838 (17.1%), 3169 patients (64.4%) and 911 patients (18.5%) (Table 1). DCIS tended to have higher HER2 expression(P=0.048). Then we compared the characteristics of HER2 0 and HER2 low in DCIS. Table 2 shows the relation between Van Nuys classification and HER2 expression. Van Nuys classification was evaluated in 346 cases. Van Nuy grade 3 accounted for 4.8% of the HER2 0 cases and 15.8% of the HER2 low cases. HER2 low cases tend to have higher grades(P < 0.01). Table 3 shows the relation between ER expression and HER2 expression. ER negative accounted for 5% of HER2 0 cases and 8.4% of HER2 low cases. ER negatives tended to be more common in Her2 low cases(P < 0.01). Conclusion: HER2 low is not considered a molecular biological classification, but rather a classification of the target of treatment for Trastuzumab deruxtecan. In our study, comparing HER2 0 and HER2 low, HER2 low tended to have higher grade and lower ER expression. Further investigation including basic research is needed to clarify the biological meaning of her2 low. Table1: The frequency of HER2 expression in DCIS and IDC Table2: The relationship between Van Nuys classification and HER2 expression Table3: The relationship between ER status and HER2 expression Citation Format: Nari Kureyama, Maho Kusudo, Akira Nakakami, Rie Komaki, Yuka Endo, Kazuki Nozawa, Ayumi Kataoka, Haruru Kotani, Akiyo Yoshimura, Masaya Hattori, Masataka Sawaki, Hiroji Iwata. The comparison of HER2 low and HER2 0 in ductal carcinoma in situ (DCIS) for breast cancer [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 PO5-01-01.

Abstract PO1-15-10: Lower pre-treatment B-cell gene expression signatures correspond with improved overall survival with palbociclib + endocrine therapy in HR+/HER2- metastatic breast cancer: a biomarker analysis from the GEICAM/2013-02 PEARL trial

Abstract Introduction: CDK4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) is standard-of-care for HR+/HER2- metastatic breast cancer (MBC), but little is known about which gene expression and microenvironment features are associated with benefit from CDK4/6i or differentiate response compared to chemotherapy. We examined the relationship of gene expression signatures (GES) to progression-free (PFS) and overall survival (OS) in the GEICAM/2013-02 PEARL phase III randomized study of palbociclib + ET vs. capecitabine in aromatase inhibitor-resistant HR+/HER2- MBC (NCT02028507). Methods: RNA sequencing (RNAseq) was performed on baseline tumor samples from 328 patients. Intrinsic subtype was derived by the PAM50 predictor after HER2/estrogen receptor subgroup-specific normalization. Correlations to intrinsic subtype signatures, PAM50 proliferation signature, CCNE1 expression, and 10 GES were selected for analysis. After excluding 15 Normal-like samples, Cox models were fitted for PFS and OS endpoints on each selected variable for the combined study population as well as for each treatment arm, adjusted for disease site, prior ET sensitivity, prior chemotherapy for MBC, number of involved sites, treatment arm, and intrinsic subtype. P-values were adjusted based on the Bonferroni method, with an adjusted p-value < 0.05 defined as significant. Results: PAM50 intrinsic subtype (54.95% Luminal A, 38.98% Luminal B and 6.07% non-luminal (4.79% Her2-enriched and 1.28% Basal-like)) was associated with worse PFS with palbociclib + ET for non-luminal vs. Luminal A tumors (HR 3.19, 95% CI 1.65-6.16) and for Luminal B vs. Luminal A tumors (HR 1.90, 95% CI 1.28-2.82). PAM50 luminal status (Luminal A vs. Luminal B vs. non-luminal) was significantly associated with PFS with palbociclib + ET (p=0.0003) but not capecitabine (p=0.89). In the palbociclib + ET arm, lower expression of two B-cell-associated signatures (BCAS) correlated with improved OS - the Immune1 TCGA BRCA GES (PMID: 32573490) (HR 1.52, 95% CI 1.20-1.92, p=0.009) and the B-cell/T-cell cooperativity GES (PMID: 31730857) (HR 1.42, 95% CI 1.14-1.79, p=0.04). Interaction analysis for OS showed that when stratified by low and high expression using the median, the Immune1 TCGA BRCA GES had a significant interaction with treatment arm (p=0.014). On comparison of outcomes between treatment arms, low Immune1 TCGA BRCA GES expression was significantly associated with improved OS with palbociclib + ET compared to capecitabine (HR 0.44, 95% CI 0.26-0.74, p=0.03), whereas high expression was not associated with a significant OS difference (HR 1.73, 95% CI 1.07-2.79, p=0.40). Further exploratory analysis of 164 immune GES found that, after adjustment for confounders, the top eight GES associated with OS with palbociclib + ET were BCAS (unadjusted p-values < 0.005), including our pre-selected Immune1 TCGA BRCA and B-cell/T-cell cooperativity GES, and all eight negatively correlated with OS. In the capecitabine arm, this exploratory analysis failed to demonstrate a similar association between the immune GES and OS. Conclusion: PAM50 intrinsic subtype was significantly associated with PFS with second-line palbociclib + ET. Lower expression of BCAS was associated with improved OS outcomes with palbociclib + ET independent of intrinsic subtype, and for the Immune1 TCGA BRCA GES, lower expression corresponded with improved OS with palbociclib + ET compared to capecitabine. This informs recent findings that in HR+/HER2- breast cancer, tumor immune activity may be a negative predictor of CDK4/6i benefit. Citation Format: Yash Agrawal, Aranzazu Fernandez-Martinez, Miguel Gil-Gil, Christoph Zielinski, Manuel Ruíz- Borrego, Eva Ciruelos, Montserrat Muñoz, Mireia Margelí, Begoña Bermejo, Antonio Antón, Zsuzsanna Kahan, Tibor Csöszi, José L Alonso-Romero, Jose Angel García-Sáenz, Pedro Sánchez-Rovira, Elena Álvarez, J. Ignacio Chacón, Santiago González-Santiago, César A Rodríguez, Sonia Servitja, Adam D. Pfefferle, Jesús Herranz, Yuan Liu, Lisa A. Carey, Isabel Romero - Camarero, Rosalía Caballero, Charles M. Perou, Miguel Martín. Lower pre-treatment B-cell gene expression signatures correspond with improved overall survival with palbociclib + endocrine therapy in HR+/HER2- metastatic breast cancer: a biomarker analysis from the GEICAM/2013-02 PEARL 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 PO1-15-10.

Abstract PS12-02: Exploration of ctDNA Dynamics in the PACE Trial: A Randomized Phase II Study of Fulvestrant, Palbociclib, and Avelumab for HR+/HER2- Metastatic Breast Cancer

Abstract Background The PACE trial for HR+/HER2- metastatic breast cancer (MBC) prospectively evaluated whether continuation of the CKD4/6 inhibitor (CDK4/6i) palbociclib (P) beyond progression on prior CDK4/6i and aromatase inhibitor (AI), with a change in endocrine therapy (ET) to fulvestrant (F), improved outcomes beyond change to F alone, as well as explored the activity of a palbociclib, fulvestrant, and avelumab (P+F+A) triplet. The primary analysis did not show improvement in progression-free survival (PFS) with F+P versus F alone. In this analysis, an evaluation of serial translational PACE samples was performed to gain insights into the mutational landscape of HR+/HER2- MBC after prolonged exposure to CDK4/6i, evaluate early mutational dynamics with ongoing therapy, and identify potential genetic markers predictive of treatment response. Additionally, the identification of acquired mutations at the time of tumor progression could provide valuable information about mechanisms of treatment resistance. Methods PACE is a multicenter randomized open-label investigator-initiated phase II trial. Eligible patients (pts) had HR+/HER2- evaluable MBC with prior progression on AI and any CDK4/6i after > 6 months (mo) of therapy in the MBC setting, or during/within 12 mo in the adjuvant setting, with no more than 1 prior line of chemotherapy for MBC. Pts were randomized 1:2:1 to F alone, F+P, or F+P+A, with tumor assessments every 8 weeks. Correlative samples including circulating tumor DNA (ctDNA) were collected at baseline (BL), times of tumor assessments (C3D1), and end of study/progression (EOT). Targeted NGS (Guardant360) to evaluate mutations (somatic single nucleotide variants and indels) was performed. Kaplan-Meier survival curves were used for assessing PFS and the log-rank test for comparisons. McNemar’s test with continuity correction was used to test the changes in the frequency of mutations. Results Of the 220 randomized pts, 211 contributed ctDNA samples (200 at BL, 129 at C3D1, 146 at EOT). Characteristics of the correlative science population were similar to the intention to treat population. At BL, the most common mutations observed were ESR1 (57%), TP53 (38%), PIK3CA (36%), GATA3 (20%) ATM (12%) and Rb1 (12%). The presence of a PIK3CA mutation vs WT-PIK3CA at BL was associated with shorter PFS in the F alone arm (p=0.001) but not in the F+P or F+P+A arms. ESR1 mutations present at baseline were D538G (34%), Y537S (21%), Y537N (15%), E380Q (10%) and L536H (4%). At C3D1, the most common mutations observed were ESR1 (47%), TP53 (33%), PIK3CA (26.1), GATA3 (18.1), ATM (13%) and PTEN (8.6%). Including only BL and C3D1 matched samples (N=124), the prevalence of ESR1 mutations decreased after 2 cycles of treatment (57% at BL vs 44% at C3D1), predominantly observed in the F+P+A arm. For those in any arm with at least 6 months of disease stability on study (N=53), the presence of an ESR1 D538G mutation decreased during therapy, with 38% having a mutation at BL, 24% at C3D1, and no pts gaining ESR1 D538G at C3D1. The prevalence of PIK3CA mutations also decreased on treatment (32% at BL to 24% at C3D1), with the greatest decrease in the F+P arm. A predictive model correlating early genomic dynamics and associations with outcome will be presented. Conclusions The PACE trial offers one of the largest clinical trial cohorts describing the genomic landscape of HR+/HER2- MBC post-CDK4/6 exposure. Results from this correlative study provide a comprehensive mutational landscape post-CDK4/6i, demonstrate associations between mutations and clinical outcomes, and suggest the potential value of early ctDNA dynamics in this setting. Citation Format: Rinath Jeselsohn, Jingxin Fu, Yue Ren, Reshma Mahtani, Cynthia Ma, Angela DeMichele, Massimo Cristofanilli, Jane Meisel, Kathy Miller, Yara Abdou, Elizabeth Riley, Rubina Qamar, Priyanka Sharma, Sonya Reid, Naomi Ko, Yuan Liu, Harold Burstein, Michelle DeMeo, Sara Tolaney, Erica Mayer. Exploration of ctDNA Dynamics in the PACE Trial: A Randomized Phase II Study of Fulvestrant, Palbociclib, and Avelumab for HR+/HER2- Metastatic Breast Cancer [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 PS12-02.

Abstract PO1-05-12: Pooled clinical trial data analyses comparing the biology of HER2-low vs HER2-0 breast cancer in patients with metastatic breast cancer following treatment with standard single agent chemotherapy

Abstract Background: Prior analyses of observational data suggest that for patients with metastatic breast cancer (MBC), tumor biology does not vary by HER2-low vs. HER2-0 expression given similar overall survival (OS) times after accounting for patients’ clinicopathologic features including hormone receptor (HR) status. We sought to evaluate potential differential biology by HER2-low status by (1) studying data pertaining to patients treated in historic clinical trials (i.e., data collected to measure associations between protocol defined treatments and outcomes) and (2) evaluating the endpoint of progression-free survival (PFS) in addition to OS following treatment with standard single agent chemotherapy for MBC. Methods: Pooling anonymized clinical trial data from studies within the Medidata Enterprise Data Store, we identified 142 women with HER2-negative MBC who received treatment with an NCCN recommended single agent chemotherapy in the context of a clinical trial. Using patient-level immunohistochemistry (IHC) results, we categorized patients as either HER2-low (IHC 1+/2+ and not amplified by in situ hybridization) or HER2-0 (IHC 0). We compared patients’ baseline demographic and clinicopathologic features according to HER2-low vs HER2-0 status. We used Cox proportional-hazard models stratified by HR status to estimate OS and PFS according to HER2-low vs HER2-0 classification while adjusting for patients' baseline demographic and clinicopathologic attributes. Results: Patients with HER2-low disease represented 20% (28/142) of the HER2-negative cohort. Twenty-five percent (7/28) of HER2-low patients had tumors that expressed hormone receptors compared with 17% (19/114) of HER2-0 patients (p=0.31). In this cohort, the maximum follow up time was 38.4 months. For HER2-low patients vs HER2-0 patients, the median OS was 10.7 vs. 12.7 months (p=0.37), and the median PFS was 3.5 vs. 2.9 months (log rank test, p=0.53) respectively. In Cox proportional-hazard models that adjusted for patient demographic and clinicopathologic features and were stratified by HR status, patients with HER2-low tumors had an 16% elevated (non-significant) hazard of death compared with patients with HER2-0 tumors (HR 1.16, 95% CI: 0.69-1.95) and a 22% reduced (non-significant) hazard of progression or death (HR 0.78, 95% CI: 0.45-1.35). Conclusions: Analyses of pooled historic clinical trial data pertaining to women with HER2-negative MBC who were treated with single agent chemotherapy revealed no meaningful clinical differences in either OS or PFS endpoints according to HER2-negative subtypes (i.e., HER2-low vs. HER2-0) after accounting for patient demographic and clinicopathologic features. These results support prior findings from observational research suggesting that there are no biological differences associated with HER2-negative subtypes. Table. Multivariable Cox Proportional Hazards Models for OS and PFS Stratified by Hormone Receptor Status, (N=134) Variable OS PFS HR* 95% CI HR* 95% CI Age (decade) 0.84 0.70-1.01 0.86 0.72-1.01 Race White 1.00 (referent) 1.00 (referent) Black 1.75 0.84-3.63 1.57 0.66-3.73 Asian 0.93 0.47-1.80 1.33 0.71-2.51 Other 1.69 0.45-6.38 2.10 0.62-7.15 Ethnicity Non-Hispanic or Latino 1.00 (referent) 1.00 (referent) Hispanic or Latino 2.10 0.95-4.64 1.02 0.44-2.35 HER2 Characterization HER2-0 1.00 (referent) 1.00 (referent) HER2-1+/2+ 1.16 0.69-1.95 0.78 0.45-1.35 Prior Lines of Chemotherapy for Metastatic Disease 0 1.00 (referent) 1.00 (referent) 1 0.82 0.46-1.46 1.13 0.65-1.95 2 0.69 0.35-1.36 1.00 0.52-1.93 3 0.59 0.10-3.42 2.18 0.45-10.50 ECOG Performance Status 0 1.00 (referent) 1.00 (referent) 1 1.65 1.07-2.54 1.57 1.02-2.43 Legend: OS=overall survival; PFS=progression-free survival; HR=hazard ratio; HER2=human epidermal group factor receptor 2; ECOG=Eastern Cooperative Oncology Group. *Analyses adjusted for clinical trial membership (coefficients not reported) Citation Format: Elizabeth Lamont, Emily Stein, Paolo Tarantino, Sara Tolaney, Corinne Ahlberg, Krishna Chinnathambu, Jiezhi Qi, Kala Tummagunta, Jackie Bilan, Ruthanna Davi, Lisa Ensign. Pooled clinical trial data analyses comparing the biology of HER2-low vs HER2-0 breast cancer in patients with metastatic breast cancer following treatment with standard single agent chemotherapy [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 PO1-05-12.

Recurrent severe hypocalcemia following chemotherapy regimen changes in advanced breast cancer: two case reports

BackgroundAs an oncologic emergency related to abnormalities in calcium metabolism, hypercalcemia associated with paraneoplastic syndrome and bone metastases is well known. Meanwhile, the incidence of hypocalcemia is low, except in cases associated with bone-modifying agents used for bone metastases. Hypocalcemia induced by bone-modifying agents typically occurs early after the initial administration, and its incidence can be significantly reduced by preventive administration of calcium and vitamin D3 supplements.Case reportWe report two cases of recurrent severe hypocalcemia occurring during chemotherapy for metastatic breast cancer with multiple bone metastases.Case 1: A 35-year-old Japanese woman developed metastases in the bone, liver, and ovaries during postoperative endocrine therapy for invasive lobular carcinoma of the breast. She underwent chemotherapy and treatment with denosumab. She experienced recurrent episodes of severe hypocalcemia subsequent to a change in the chemotherapy regimen. Case 2: A 65-year-old Japanese woman encountered multiple bone metastases after postoperative anti-human epidermal growth factor receptor 2 therapy and during endocrine therapy for invasive ductal carcinoma of the breast. She underwent anti-human epidermal growth factor receptor 2 therapy and treatment with denosumab. She experienced recurrent severe hypocalcemia subsequent to a change in the chemotherapy regimen to letrozole + lapatinib, trastuzumab emtansine, and lapatinib + capecitabine.ConclusionsWe observed two cases of recurrent severe hypocalcemia in patients with advanced breast cancer and bone metastases after modifications to their therapy regimens. These cases differed from the typical hypocalcemia induced by bone-modifying agents. It is possible that antitumor drugs affect calcium and bone metabolism associated with bone metastases. While these cases are rare, it is crucial for oncologists to be aware of hypocalcemia not only at the initiation of bone-modifying agents but also throughout the entire antitumor therapy, as hypocalcemia can lead to fatal outcomes.

Efficacy and safety of nanoparticle albumin-bound paclitaxel in taxane-pretreated metastatic breast cancer patients.

Taxanes are the basic components of breast cancer chemotherapy. Nanoparticle albumin-bound paclitaxel (nab-paclitaxel) shows improved antitumor effects because of more targeted delivery. However, the effects of nab-paclitaxel have not been systematically studied in patients with metastatic breast cancer (MBC) pretreated with taxanes. Considering the limited treatment options for MBC, this study retrospectively evaluated the clinical efficacy and adverse effects of nab-paclitaxel in patients with taxane-pretreated MBC. Patients who had previously received taxanes and subsequently received nab-paclitaxel chemotherapy for MBC at Jiangsu Cancer Hospital between October 2014 and April 2022 were included for analysis. The primary end point was progression-free survival (PFS), and the secondary end points were the objective response rate (ORR), disease control rate (DCR), clinical benefit rate (CBR), and side effects. A total of 236 female patients with MBC were included. The median PFS was 7.20months (95% confidence interval [CI], 6.63-7.80months), and the ORR, DCR, and CBR were 29.55% (95% CI, 23.50%-35.60%), 83.64% (95% CI, 78.70%-88.60%), and 56.36% (95% CI, 49.80%-63.00%), respectively. Following nab-paclitaxel treatment, the median PFS of patients who were sensitive to taxanes during previous treatments was significantly longer than that of patients who were resistant to taxanes (7.57months vs. 4.43months, p<.001). The most common adverse events were sensory neuropathy (89.83%), neutropenia (48.73%), leukopenia (46.61%), and anemia (35.59%). Nab-paclitaxel demonstrated clinical activity in taxane-pretreated patients with MBC. This beneficial effect was observed both in patients who were sensitive and resistant to taxanes during previous treatments. These results suggest nab-paclitaxel as the preferred chemotherapy regimen in patients with MBC, regardless of their sensitivity to taxanes during previous treatments.

A Cohort Study of the Antitumor Efficacy and Toxicity Profile of Alpelisib for Metastatic or Locally Advanced HR+, HER2− Breast Cancer: A Single-Institution Experience

Introduction: Alpelisib is approved in combination with endocrine therapy (ET) to treat patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) progressive metastatic breast cancer (MBC). The SOLAR-1 trial demonstrated the efficacy of this oral agent and showed that, while alpelisib improves outcomes compared to placebo, it is also associated with clinically relevant adverse events (AEs). There is a pressing need for improved knowledge on the effectiveness and tolerability of this agent in real-world patient populations. Methods: We conducted a retrospective cohort study of patients with HR+, HER2− MBC treated with alpelisib and ET. We assessed the safety, tolerability, and effectiveness of alpelisib in a real-world population. Deidentified patient-, tumor-, and outcome-related data, including AEs, were collected and summarized. Kaplan-Meier methods were applied for survival analyses, and stratified analyses of interest were conducted. A p value <0.05 was considered statistically significant. Results: A total of 76 women treated with alpelisib + ET were included in our cohort. Most had been previously treated with cyclin-dependent kinase (CDK) 4/6 inhibitors and chemotherapy for MBC. The estimated median progression-free survival was 5.2 months (95% CI, 4.1–8.0). The median overall survival was longer among patients without prior everolimus therapy (hazard ratio, 4.28 [95% CI, 1.64–11.16]; p = 0.0012), and no significant outcome differences were observed between patients treated with different starting doses of alpelisib. Approximately 31.6% of patients permanently discontinued alpelisib due to AEs, and 32.9% had at least one dose reduction. The most common grade 3/4 AEs were hyperglycemia (21%), fatigue (13.2%), and diarrhea (10.5%). Conclusions: For progressive HR+, HER2− MBC, alpelisib + ET showed effectiveness in a real-world patient population that was comparable to published clinical trial data, regardless of starting dose. However, the effectiveness of alpelisib following previous everolimus exposure may be limited and, hence, should be a consideration to decide sequencing of therapy in these patients. Patients treated with alpelisib are at risk for clinically relevant AEs and require close monitoring.

P45-5 A case report of pneumothorax after treatment with bevacizumab-containing chemotherapy for metastatic breast cancer

P45-5 A case report of pneumothorax after treatment with bevacizumab-containing chemotherapy for metastatic breast cancer

Phase II study of apatinib plus exemestane in estrogen receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer

ABSTRACT Purpose Apatinib is a tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR)-2. This study was conducted to assess the efficacy and safety of apatinib combined with exemestane in patients with estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). Methods This single-center, single-arm phase II study enrolled patients with ER+/HER2- MBC progressed on previous letrozole or anastrozole. Stratified analysis was performed according to the number of chemotherapy regimens for metastatic disease. The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (ORR), disease control rate (DCR), clinical benefit rate (CBR), overall survival (OS) and toxicity. Patients received apatinib at a starting dose of 500 mg/d and exemestane 25 mg/d on days 1–28 of each 4-week cycle. Results Thirty patients were enrolled with median four prior anticancer therapies. Eighty percent of patients received chemotherapy for metastatic disease. The median PFS (mPFS) and OS were 5.6 (95%CI: 4.3–6.9) months and 15.7 (95% CI: 9.7–21.7) months, respectively. The ORR, DCR, and CBR were 21.4%, 71.4%, and 46.4%, respectively. Patients with 0–1 line chemotherapy for MBC showed a slightly longer mPFS compared to those with ≥2 lines chemotherapy (mPFS: 6.4 months vs 4.8 months, P = .090). Most of the AEs were grade 1/2. One patient (3.3%) who suffered bone marrow metastases experienced grade 4 thrombocytopenia, and 14 experienced grade 3 AEs. Fifty percent of patients were given reduced dose for apatinib. Conclusions Apatinib plus exemestane exhibited objective efficacy in patients with ER+/HER2- MBC who have failed multiple lines of treatment. The AEs of apatinib required close monitoring and most of patients were well tolerated.

412P Sacituzumab govitecan versus chemotherapy for metastatic breast cancer: A meta-analysis on safety outcomes

412P Sacituzumab govitecan versus chemotherapy for metastatic breast cancer: A meta-analysis on safety outcomes

Cost-effectiveness of extended DPYD testing before fluoropyrimidine chemotherapy in metastatic breast cancer in the UK.

The aim of this study was to evaluate the cost-effectiveness of ToxNav©, a multivariant genetic test, to screen for DPYD followed by personalized chemotherapy dosing for metastatic breast cancer in the UK compared with no testing followed by standard dose, standard of care. In the main analysis, ToxNav© was dominant over standard of care, producing 0.19 additional quality-adjusted life yearsand savings of £78,000 per patient over a lifetime. The mean additional quality-adjusted life years per person from 1000 simulations was 0.23savings(95% CI: 0.22-0.24) at £99,000 (95% CI: £95-102,000). Varying input parameters independently by range of 20% was unlikely to change the results in the main analysis. The probabilistic sensitivity analysis showed ~97% probability of the ToxNav©strategy to be dominant.

D-dimer as a predictive biomarker of response to chemotherapy in patients with metastatic breast cancer.

e13000 Background: Tumor-induced coagulation is considerably observed in cancer patients. Moreover, it is associated with tumorigenesis, tumor progression, and metastasis, by creating a proliferative and proangiogenic microenvironment. Therefore, D-dimer, a fibrin degradation product, correlates with tumor prognosis in several cancer types. This study aims to investigate whether D-dimer levels can be a predictive and monitoring indicator for chemotherapy response in metastatic breast cancer (MBC) patients. Methods: This study included two groups, 76 patients diagnosed with metastatic breast carcinoma, and 25 with early breast carcinoma as a control group. Plasma D-dimer levels were measured prospectively before chemotherapy initiation, and after the fourth treatment cycle in MBC patients. The levels of D-dimer before chemotherapy (D0) were analyzed using receiver operating characteristic (ROC) curves to determine the optimal cutoff baseline values of D0, and to evaluate their discriminatory abilities in predicting response to chemotherapy. Results: In the preliminary response evaluation, the mean level of D-dimer significantly decreased by 2.74 μg/ml in patients with partial response, and by 2.17 μg/ml in patients with stable disease. In the progression disease group, a considerable increase was seen in D-dimer levels by 2.16 μg/ml. Analysis of ROC curves showed that D-dimer levels at D0 could discriminate the response to chemotherapy, whereas the progressive disease rate correlated with higher levels of D-dimer (&gt;1.055 μg/ml; P= 0.000). Conclusions: D-dimer level in plasma is a useful predictive and monitoring marker of response to chemotherapy in metastatic breast cancer.

The efficacy of metformin as adjuvant to chemotherapy on IGF levels in non-diabetic female patients with progressive and non-progressive metastatic breast cancer.

Some studies have shown that metformin inhibits the proliferation of breast cancer (BC) cells via multiple ways. One of these mechanisms is through the indirect control of the IGF-route mediated via the activation of the AMPK-LKB1 pathway in the liver, which leads to a decrease in blood glucose and insulin levels. The objective of this study was to investigate the effects of metformin as adjuvant to chemotherapy on IGF levels in female patients with progressive and non-progressive metastatic BC. In this trial, 107 women receiving chemotherapy for metastatic breast cancer (MBC) were divided into two groups: the metformin group received 500 mg of metformin twice daily, whereas the control group did not receive any metformin. All patients received chemotherapy according to the South Egypt Cancer Institute's (SECI) established regimen. The level of IGF-1 was determined in the blood at the initiation of therapy (baseline) and at six months post treatment. No substantial differences were noted regarding IGF-1 levels in both groups at baseline (IGF-1 average level was 40.74 ± 36.16 vs. 32.06 ± 20.00 in the metformin and the placebo group, respectively, p = 0.462). While after six months, the mean IGF-1 level was 37.62 ± 31.35 vs. 39.12 ± 2 5.93 in the metformin and placebo groups, respectively, (p = 0.170). Metformin as an adjuvant to chemotherapy in MBC patients had no significant effect on reducing IGF-l levels which promotes the inhibition of the proliferation of BC cells in MBC patients.

Harnessing olaparib, palbociclib, and endocrine therapy: A phase I/II trial of olaparib, palbociclib and fulvestrant in patients with BRCA mutation-associated, hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (HOPE).

TPS1126 Background: Hormone receptor-positive (HR+) metastatic breast cancer (MBC) in patients (pts) with germline or somatic BRCA1 or BRCA2 (g/s BRCA1/2) mutations has dual drivers: hormone receptor signaling and homologous recombination deficiency. The PALOMA-3 trial showed superiority of fulvestrant (F) with palbociclib (P) compared to F alone. The OlympiAD trial showed the poly-ADP ribose polymerase inhibitor (PARPi) olaparib (O) to be superior to chemotherapy in BRCA1/2-associated MBC. However, treatment resistance inevitably develops; targeting dual therapeutic drivers concurrently may delay or circumvent resistance. O and P have overlapping hematologic toxicity and the safety of combined O, P and F is unknown. The tolerability of O + P is particularly relevant given the emergence of potentially less myelosuppressive PARPi. Methods: HOPE (NCT03685331) is a phase I/II trial to evaluate safety and efficacy of O, P and F in pts with g/s BRCA1/2-associated, HR+ MBC. Eligible pts have an ECOG performance status 0-1, measurable/evaluable breast cancer, any/no prior endocrine therapy, and 0-2 lines of chemotherapy for MBC. Prior platinum is allowed for curative intent if completed at least 12 months prior to MBC diagnosis, or for MBC if no progression during therapy. Prior PARPi and CDK4/6i are permitted on phase I, and are permitted during phase II if there was no progression on them. Treatment (28-day cycles) consists of: O orally twice daily continuously; F 500mg intramuscularly on day 1 of each cycle plus load; and P orally once daily on days 1-21. Phase I begins with a 28-day safety run-in of O and F alone. O and P doses are based on dose level (DL): DL 0 (starting level), O 300mg, P 75mg; DL 1, O 300mg, P 100mg; DL 2, O 300mg, P 125mg; DL-1, O 250mg, P 75mg and DL-2, O 200mg, P 75mg. For phase II, O and P will be dosed at MTD. Pts have tissue collection at baseline and peripheral blood cfDNA analysis at baseline, at progression, and at all scan timepoints (every 3 cycles). Phase I primary endpoint is MTD. A 3+3 dose escalation design is used with a 30% rate of dose limiting toxicity (DLT) deemed acceptable, and 6 patients treated at a dose for it to be declared MTD. A minimum of 2 and a maximum of 18 patients will be enrolled on the phase I. Phase II primary endpoint is PFS using Kaplan-Meier methods and secondary efficacy endpoints are objective response rate and 24-week clinical benefit rate. Phase II will evaluate 54 subjects to provide 80% power to detect an increase in PFS from 7 months with O monotherapy to 10 months. Exploratory objectives include examination of baseline tissue for PARPi predictive biomarkers and measures of tumor immunogenicity as well as serial serum evaluation for reversion mutations. Enrollment is ongoing. Clinical trial information: NCT03685331 .

Circulating tumor cells (CTCs) dynamics after CDK4/6i for hormone-receptor positive (HR+) metastatic breast cancer (MBC): A biomarker analysis of the PACE randomized phase II study.

1059 Background: PACE is a multicenter randomized phase II trial investigating palbociclib (P) in combination with fulvestrant (F) after progression on any CDK4/6 inhibitor (CDK4/6i), with or without the PD-L1 inhibitor avelumab (A), in HR+/HER2- MBC. CTCs are rare cells in the blood stream whose detection is associated with worse outcome and treatment resistance. Methods: Eligible patients (pts) had HR+/HER2- MBC with prior progression after ≥ 6 months (mo) of AI and CDK4/6i for MBC, or during/within 12 mo in the adjuvant setting, with ≤ 1 prior chemotherapy for MBC. Pts were randomized 1:2:1 to F, F+P, or F+P+A. CTC detection and enumeration were performed utilizing CellSearch (Menarini Silicon Biosystems) at baseline (BL), at time of first tumor assessment (TTA1), and at progression. Results were dichotomized using the standard CTC threshold (≥ 5 CTCs/7.5 ml) into a novel prognostic classification: StageIVindolent and StageIVaggressive (Cristofanilli et al 2019). Concurrent ctDNA Sequencing was performed using Guardant360 (Guardant Health). Results: Of the 220 randomized pts, 203 (92%) had sample available for BL CTC enumeration, 155 had detectable CTCs (70.5%), and 99 (48.8%) were StageIVaggressive. De novo disease at initial diagnosis was associated with StageIVaggressive (47.5% vs 30.8% StageIVindolent), and distribution of visceral versus non-visceral disease was similar across the two CTCs groups. StageIVaggressive represented 38.3%, 54.8%, and 46.2% of the F, F+P and F+P+A treatment groups, respectively. BL CTCs were prognostic in the overall cohort; median PFS was 5.7mo vs 3.5mo for StageIVindolent vs StageIVaggressive (HR: 1.69, 90%CI 1.27,2.24, P&lt;0.001). Median PFS for the F, F+P and F+P+A arms was 1.9mo, 4.6mo and 5.4mo in StageIVaggressive compared to 8.2mo, 5.3mo and 8.3mo in StageIVindolent. Among patients in the StageIVaggressive subgroup, the F+P and F+P+A arms demonstrated improved outcomes compared to F alone. (F+P vs F HR 0.43, 90% CI 0.25-0.71, and F+P+A vs F HR 0.26, 90% CI 0.14-0.49). No benefit of F+P or F+P+A over F was observed in the StageIVindolent subgroup (F+P vs F HR 1.45, 90% CI 0.87 - 2.40 and F+P+A vs F HR 1.06, 90% CI 0.61 - 1.84, each p(interaction)&lt;0.01). Changes in StageIV CTC characterization (indolent vs aggressive) between BL and TTA1 among the subset of 175/203 pts with both timepoints available are reported. Conclusions: Baseline CTC enumeration is prognostic in patients receiving F with or without CDK4/6i. The StageIVaggressive subgroup may derive preferential benefit with combinations of F+P or F+P+A over F alone. Findings should be confirmed in other studies. ctDNA analyses are ongoing. Clinical trial information: NCT03147287 . [Table: see text]

Cyclin E cytoplasmatic isoform to predict outcome and benefit to capecitabine treatment in patients with HR+/HER2- metastatic breast cancer from the GEICAM/2013-02 PEARL study.

1023 Background: Cytoplasmic cyclin E protein expression, serving as a surrogate for the low molecular weight cyclin E isoform (LMW-E), is a biomarker associated with aggressive breast cancer and predicts resistance to aromatase inhibitors in luminal breast cancer. We investigated the prognostic and predictive value of cytoplasmic and nuclear isoforms of cyclin E in HR+/HER2- metastatic breast cancer (MBC) patients receiving palbociclib CDK4/6 inhibitor and endocrine therapy (PALBO+ET) versus capecitabine (CAPE) in the GEICAM/2013-02 PEARL trial (NCT02028507). Methods: Expression of Cytoplasmic and Nuclear isoforms of cyclin E were assessed by immunohistochemistry (IHC). An H-score based on the proportion and intensity of stained cells was explored using median value to categorize in Low / High expression the Nuclear and Cytoplasmic scores (N and C, respectively). In addition, N and C were independently assigned according to staining intensity (1 = no staining, 2 = weak, 3 = intermediate and 4 = strong staining) and then, combined in 4 phenotypes (Ph): Ph1 (N-/C-); Ph2 (N+/C-); Ph3 (N+/C+); and Ph4 (N-/C+), where negative=1-2, and positive=3-4. Cox regression models’ analysis were assessed to predict outcome and benefit to treatment, in terms of PFS and OS. Multivariate models were adjusted for confounders: age, site of disease, sites of metastasis, prior chemotherapy for MBC and treatment. Interaction analysis with treatment arm were performed. Results: Cyclin E protein was obtained from 344 tumors, with 73% being primary tumors and 27% metastatic. High expression of the Nuclear isoform was independently associated with significantly worse OS (median OS [mOS]=34.23 months [m] for low expression vs 25.72m for high expression; adjusted HR=1.48; p-value=0.016). Phenotype analysis supported this finding, with Ph3 (N+/C+) and Ph4 (N-/C+) demonstrating the worst (mOS=19.55m) and best (mOS=37.19m) outcomes, respectively (using Ph1 as reference, Ph3 HR=2.92; p-value=0.0013). The interaction between the treatment arm and Cytoplasmic cyclin E expression was significant (p=0.0052). Patients with high expression of the Cytoplasmic isoform had significantly better PFS with CAPE (mPFS=14.8m) than with PALBO + ET (mPFS=5.73m) (HR=1.9, p-value=0.0418). Ph4 (N-/C+) had also significantly better PFS for CAPE (mPFS=22.67m) than for PALBO + ET (mPFS=8.51m) (HR=2.94; p-value=0.036). Conclusions: This study confirms Cyclin E as a poor prognostic marker associated with worse overall survival in luminal MBC patients. Low molecular weight Cyclin E, detected as Cytoplasmic Cyclin E, identifies luminal MBC that benefit more from CAPE than from PALBO + ET. The low molecular weight Cyclin E isoform appears to be a promising predictive biomarker for the benefit of CAPE and resistance to PALBO + ET treatments in this population. Clinical trial information: NCT02028507 .

Treatment of palbociclib in hormone receptor positive breast cancer: a real-world study and efficacy prediction model

Objective: To summarize the clinical use of palbociclib and evaluate its efficacy and safety in hormone-receptor (HR)-positive advanced breast cancer patients. Methods: We retrospectively analyzed data from 66 HR-positive metastatic breast cancer patients treated with palbociclib and endocrine therapy at the Department of Oncology in the First Affiliated Hospital with Nanjing Medical University between 2018 and 2020. We evaluated the factors affecting the efficacy of palbociclib using Kaplan-Meier method and Log-rank test for survival analysis and Cox regressions for multivariate analysis. Nomogram model was built for predicting prognosis among HR-positive breast cancer patients who received palbociclib. Concordance index (C-index) and calibration curve were used for internal validation to assess the predictive ability and conformity of the model. Results: Of the 66 patients treated with palbociclib, 33.3%(22), 42.4%(28) and 24.2%(16) patients were treated without endocrine therapy, first-line endocrine therapy, second-line or above endocrine therapy after recurrence, respectively. 36.4%(24) patients had hepatic metastasis, 16.7% (11) patients were sensitive to previous endocrine therapy, 27.3%(18/66) patients had primary resistance to endocrine therapy, while 56.1% (37) patients had secondary resistance to endocrine therapy. The overall response rate was 14.3% (95% CI: 6.7%, 25.4%) and clinical benefit rate was 58.7% (95% CI: 45.6%, 71.0%). Better clinical outcomes were associated with non-hepatic metastasis (P=0.001), sensitive/secondary resistant to previous endocrine therapy (P=0.004), no or only one line of chemotherapy for metastatic breast cancer (P=0.004), recent pathological confirmation of immunohistochemical analysis (P=0.025). Hepatic metastasis (P=0.005) and primary resistance to endocrine therapy (P=0.016) were the independent risk factors of progression free survival. The C-index of predictive probability for the nomogram constructed from the patient clinical characteristics (whether liver metastasis, whether primary endocrine resistance, lines of chemotherapy after metastasis, lines of endocrine therapy, number of metastatic sites, and time to last immunohistochemistry) to predict the progression-free survival at 6 and 12 months for patients was 69.7% and 72.1%, respectively. The most common adverse events were hematologic toxicities. Conclusions: Our report indicates that palbociclib combined with endocrine therapy for HR-positive recurrent metastatic breast cancer is effective and safe; patients with hepatic metastases and primary resistance to endocrine therapy have worse prognoses and are independent risk factors for progression after palbociclib therapy. The constructed nomogram could help predict the survival and guide the use of palbociclib.

Abstract P3-06-02: TATEN TRIAL (SOLTI-1716) Targeting non-Luminal disease by PAM50 with pembrolizumab + paclitaxel in Hormone Receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC): interim analysis

Abstract Background Within HR+/HER2- disease, patients with non-luminal subtypes of breast cancer (HER2-enriched [HER2-E] and Basal-like) have poorer prognosis than those with luminal subtypes, may be more sensitive to chemotherapy, and have higher expression of immune-related genes and tumor infiltrating lymphocytes (TILs). Here, we report the interim efficacy and safety data of the TATEN trial (NCT04251169), the first study designed to evaluate pembrolizumab and paclitaxel in HR+/HER2-negative, PAM50 non-luminal, metastatic breast cancer (MBC). Methods TATEN is a single-arm, multicenter phase II study evaluating pembrolizumab in combination with paclitaxel in patients with HR+/HER2-, PAM50 non-luminal, MBC. Key inclusion criteria include progression to prior CDK4/6 inhibitors, presence of measurable disease by RECIST V1.1, no prior chemotherapy for MBC, and ECOG 0-1. Patients receive pembrolizumab at 200 mg every 3 weeks (on D1 of each 21-day cycle, beginning at cycle 1) in combination with weekly paclitaxel at 80 mg/m2, beginning at cycle 2. The primary endpoint is to evaluate overall response rate (ORR), defined as the rate of complete (CR) and partial response (PR) according to RECIST V1.1. Secondary endpoints include clinical benefit rate (CBR; CR + PR + stable disease &amp;gt;24 weeks), progression free survival, overall survival, safety, and predictive biomarkers. Tumor samples collected during advanced/metastatic disease are mandatory to assess PAM50 and other translational endpoints. This study had a planned interim analysis after 15 patients were evaluable for ORR based on a Simon’s two stage design with 80% power and a type I error rate of 0.05. Stage I of the trial would be considered successful if at least 6 patients achieved a PR and/or CR. In that case, the trial would recruit up to 46 evaluable patients for a target ORR ≥ 41. Here we report results from the patients who received at least one dose of combination treatment and had a first, post-baseline, tumor assessment according to RECIST v1.1 (evaluable population). Results From July 2020 to December 2021, 119 patients were screened, and 25 PAM50 non-luminal tumors were identified (21%). From these, 17 (68%) patients were recruited, and 15 were evaluable for primary endpoint. Two patients discontinued the trial before the first dose of pembrolizumab and paclitaxel, because of clinical progressive disease (PD). Baseline patient characteristics were as follows: median age 53 years (range: 40-77), ECOG 0 52.9%, de novo MBC at diagnosis 29.4%, and visceral disease 64.7% (including 53.3% with liver metastasis). Ten patients had received paclitaxel treatment in the adjuvant setting. Regarding PAM50 intrinsic subtype, two patients had basal-like and 13 HER2-E tumors. At the time of data cut-off (May 17,2022), 8 patients (53.3%) had stopped their treatment because of PD and 2 (13.3%) due to toxicity. Five patients (33.3%) were still on treatment. The ORR was 53.3 % (8 of 15, 95% CI 26.6-78.7), meeting the pre-specified ORR for the first stage of the trial. The CBR was 86.6% (13 of 15, 95%CI 59.5-98.34), and median PFS was 7.5 months (95% CI: 5.6 – 10.2). Overall, all patients experienced treatment-related adverse events (TRAEs) of any grade, while 53.3% of patients experienced grade 3 TRAEs. No grade 4 or 5 TRAEs were reported in the evaluable population. Correlative analysis including gene expression analysis and centralized TILs scoring and PD-L1 IHC will be presented. Conclusions The first stage of TATEN combining pembrolizumab with paclitaxel after progression to CDK4/6 inhibitors in patients with HR+/HER2-negative, PAM50 non-luminal MBC met its pre-specified endpoint. Completion of the stage II part of the trial with the inclusion of up to 46 patients is warranted to assess the activity of this combination in this group of patients. Correlative studies to find predictive biomarkers of response to this regimen are ongoing and will be presented at the meeting. This study was funded by MSD. Citation Format: Aleix Prat, Tomás Pascual, Montserrat Muñoz, Cristina Hernando, Silvia Vazquez, Salvador Blanch, Manuel Alva, Mafalda Oliveira, Esther Sanfeliu, Lorea Villanueva, Fara Brasó-Maristany, Nuria Chic, Eva Ciruelos. TATEN TRIAL (SOLTI-1716) Targeting non-Luminal disease by PAM50 with pembrolizumab + paclitaxel in Hormone Receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC): interim analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-06-02.