Hormone Receptor-positive HER2-negative Breast Cancer Research Articles

MAP3K1 mutations confer tumor immune heterogeneity in hormone receptor-positive HER2-negative breast cancer.

Hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer, the most common type of breast cancer, is facing challenges such as endocrine therapy resistance and distant relapse. Immunotherapy has shown progress in treating triple-negative breast cancer, but immunological research on HR+/HER2- breast cancer is still in its early stages. Here, we performed a multi-omics analysis of a large cohort of HR+/HER2- breast cancer patients (n = 351) and revealed that HR+/HER2- breast cancer possessed a highly heterogeneous tumor immune microenvironment. Notably, the immunological heterogeneity of HR+/HER2- breast cancer was related to MAP3K1 mutation and we validated experimentally that MAP3K1 mutation could attenuate CD8+ T cell-mediated antitumor immunity. Mechanistically, MAP3K1 mutation suppressed MHC-I-mediated tumor antigen presentation through promoting the degradation of antigen peptide transporter 1/2 (TAP1/2) mRNAs, thereby driving tumor immune escape. In preclinical models, the postbiotics tyramine could reverse the MAP3K1 mutation-induced MHC-I reduction, thereby augmenting the efficacy of immunotherapy. Collectively, our study identified the vital biomarker driving the immunological heterogeneity of HR+/HER2- breast cancer and elucidated the underlying molecular mechanisms, which provided the promise of tyramine as a novel therapeutic strategy to enhance the efficacy of immunotherapy.

New treatment strategy for early hormone receptor-positive HER2-negative breast cancer: updated results of adjuvant abemaciclib trial in operable and locally advanced breast cancer

Abemaciclib is an oral inhibitor 4 and 6 (CDK4/6). Abemaciclib differs from other drugs in this group in suppression spectrum of cyclin-dependent kinases and is proven to improve survival rates in different treatment lines of metastatic breast cancer. In randomized clinical trials 3rd phase in patients with early hormone-dependent HR+ HER2 negative breast cancer high risk of progression abemaciclib in conjunction with hormone therapy significantly improves invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS). Long- term outcome studies monarchE with 5 – year follow – up of patients showed that abemaciclib adding to ET increases 5-year IDFS from 76 to 83.6% (HR0.680; 95% CI 0.599 to 0.772; p <0.001) and 5-year DRFS from 79.2% to 86.0% (HR0.675; 95% CI 0.588 to 0.774; p <0.001). Adverse events of 3rd degree and higher are registrated in 45.5% of patients in abemaciclib group and in 12,7% in control group and mainly presented by neutropenia (18.6 and 0.7%) and diarrhea (7,6 and 0.1%). Toxicity profile was expected and controlled. The reasonable dose reduction of abemaciclib did not lead to deterioration of long-term treatment result.

Cyclin-dependent kinase 4/6 inhibitors combined with stereotactic ablative radiotherapy in oligometastatic HR-positive/HER2-negative breast cancer patients.

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have significantly improved the survival of patients with hormone receptor-positive HER2-negative advanced breast cancer (ABC). Although stereotactic ablative radiotherapy (SABR) is used more often in routine clinical practice, data on the safety and efficacy of combining SABR with CDK4/6i are lacking. Herein, we present the results of SABR combined with CDK4/6i in ABC. Patients with ABC who received CDK4/6i and SABR between 2018 and 2023 were analysed. Among 384 patients treated with CDK4/6i, 34 patients received 44 courses of SABR. Two-year progression-free survival (PFS) was 63.6% (95% CI, 45.8-88.3), and the median PFS was 32 months. Three-year overall survival (OS) was 88.9% (95% CI, 77.7-100). Two-year local control (LC) was 92.7% (95% CI, 83.4-100). Median OS and LC were not reached. The subgroup analysis showed the difference in survival between oligometastatic patients (OMD) and non-OMD subgroup. Two-year PFS was 69.2% (95% CI, 44.5-100) in OMD compared with 57.4% (95% CI, 36-91.7) in the non-OMD (P = .042). Three-year OS was 90% (95% CI, 73.2-100) in OMD compared with 86.2% (95% CI, 70-100) in the non-OMD (P = .67). Median PFS and OS in the non-OMD were 26 and 56 months, respectively, and were not reached in OMD. Fifteen patients required CDK4/6i dose reduction, and 2 discontinued treatment due to toxicity. No difference in high-grade toxicity was observed between the sequential and concurrent SABR. The addition of SABR to CDK4/6i seems to be safe and effective, especially in patients with oligometastatic disease. In advanced breast cancer patients treated with CDK4/6i, SABR provides a high local control and may provide additional benefit in an oligometastatic setting.

Predictors of response and surgical approach after neoadjuvant chemotherapy in receptor-positive/HER2-negative stage II-III breast cancer patients treated in two private cancer care centers in Lima, Peru: Real-world data.

e12659 Background: The role of neoadjuvant chemotherapy (NAC) in hormone receptor-positive HER2-negative breast cancer (BC) is controversial, its main benefit being to improve the surgical outcome in both breast and axilla. The aim of this study was to evaluate the response to NAC, as well as possible predictors and the type surgery performed after primary treatment. Methods: Observational, retrospective study from a database of 1356 consecutive cases of BC between 2016 and 2022 in two private oncology centers in Lima Metropolitana. There were 726 new cases of hormone receptor-positive HER2-negative BC (53.5%), of which those patients with clinical stage II-III who received NAC were considered (n=122, 16.8 % of luminal HER2-negative). Results: The average age of the sample was 46.6 years (range 25-72) with a predominance of luminal B subtype (60.7%) and clinical stage II disease (51.6%), as well as an average delay time to treatment of 33.9 days. Chemotherapy choice was AC every 3 weeks followed by weekly paclitaxel (98.4%). The pathological complete response (pCR) rate was of 16.4% in the breast, 29.1% in the lymph nodes and 13.9% in both. None of the variables studied (age, histologic grade and type, clinical stage, tumor size, number of nodes, hormone receptors, Ki-67 and HER2 low) were predictors of pCR. According to RECIST criteria, tumor shrinking in the breast occurred in the majority of patients (partial and complete response: 86.1%) and eight out of ten patients achieved a tumor size reduction of more than 50%. The rate of mastectomy was 67.2% and radical axillary dissection, 70.5%. Conclusions: In our cohort, we found a pCR rate similar to that reported in the world literature. No predictors of pCR were found. Despite the high proportion of tumor response at breast and node level, the surgical approach was mostly radical. The multidisciplinary BC committee in our setting should be strengthened in order to make better decisions on the surgical approach for patients with hormone receptor-positive HER2-negative stage II-III BC who receive NAC.

Analysis of the sensitivity to endocrine therapy (SET) assay in the PALLAS adjuvant trial of palbociclib in HR+/HER2- breast cancer (ABCSG-42/AFT-05/BIG-14-13).

538 Background: The phase 3 PALLAS trial compared 2 years of the CDK4/6 inhibitor palbociclib with endocrine therapy of provider choice, versus endocrine therapy alone, as adjuvant treatment for patients (pts) with Stage II-III hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer. The SET2,3 index adjusts the measurement of SETER/PR index of endocrine receptor-related transcriptional activity with a baseline prognostic index (BPI) derived from tumor size (T), number of involved lymph nodes (N) and gene expression levels of ESR1, PGR, ERBB2 and AURKA (RNA4 subtype score). High SET2,3 (index ≥ 2.10) represents high endocrine sensitivity with favorable prognosis. Clinical outcome results from PALLAS were previously published, and the trial now has 5-year median follow-up. Methods: Participants in PALLAS provided a tumor tissue block prior to randomization. RNA was extracted from samples with sufficient tumor tissue and cellularity (>25mm2 with ≥20% cancer nuclei). SET2,3 index was measured from 300ng total RNA using the QuantiGene Plex platform (ThermoFisher, Waltham, MA) following the manufacturer’s protocol and using pre-defined quality control (QC) parameters and cut point. Results from primary tumor samples prior to systemic therapy were analyzed. Invasive disease-free survival (iDFS) was summarized with Kaplan-Meier plots using log-rank test. Cox models were adjusted for treatment arm assignment, with a treatment arm by SET index value interaction term to test for prediction of palbociclib benefit. The pre-defined level of significance was a two-sided 0.05. Results: There were 4075 pts from the total PALLAS population (N=5796) who provided a primary tumor sample that met pre-analytical requirements to perform the SET assay, from which 3388 (83%) results passed quality control, including 3093 from a sample obtained prior to receiving systemic therapy (1559 in palbociclib arm and 1534 in the control arm). SET2,3 index could not be calculated for 12 pts due to missing tumor or nodal information. There was no evidence of an interaction between treatment arm and SET indices (continuous) for iDFS: SET2,3 index interaction p=0.12 and SETER/PR index interaction p=0.92. Estimated 5-year iDFS was superior for those with high SET2,3: iDFS was 91.4% (95%CI 89.9–92.8) in 1719 (55.8%) pts with high SET2,3, versus 78.5% (95%CI 76.0–80.8) in 1362 (44.2%) pts with low SET2,3 (HR 0.38, 95%CI 0.31–0.47, p<0.0001). The SETER/PR index was also significantly associated with iDFS (HR 0.70 per 0.5 units, 95%CI 0.65–0.77, p<0.0001). Conclusions: There was no evidence that the SET2,3 or SETER/PR index of endocrine-related transcriptional activity predicts benefit from palbociclib treatment. SET2,3 index was strongly prognostic for pts with Stage II-III breast cancer, with excellent 5-year IDFS for pts classified as SET2,3 high. Clinical trial information: NCT02513394 .

Outcomes in Nonmetastatic Hormone Receptor-Positive HER2-Negative Pure Mucinous Breast Cancer: A Multicenter Cohort Study.

Although considered a favorable subtype, pure mucinous breast cancer (PMBC) can recur, and evidence for adjuvant therapy is limited. We aimed to compare outcomes of nonmetastatic PMBC with invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) to address these uncertainties. Individual patient-level data from 6 centers on stage I-III hormone receptor-positive and HER2-negative PMBC, IDC, and ILC were used to analyze recurrence-free interval (RFI), recurrence-free survival (RFS), and overall survival (OS), and to identify prognostic factors for PMBC. Data from 20,684 IDC cases, 1,475 ILC cases, and 943 PMBC cases were used. Median follow-up was 6.6 years. Five-year RFI, RFS, and OS for PMBC were 96.1%, 94.9%, and 98.1%, respectively. On multivariable Cox regression, PMBC demonstrated superior RFI (hazard ratio [HR], 0.59; 95% CI, 0.43-0.80), RFS (HR, 0.70; 95% CI, 0.56-0.89), and OS (HR, 0.71; 95% CI, 0.53-0.96) compared with IDC. ILC showed comparable outcomes to IDC. Fewer than half (48.7%) of recurrences in PMBC were distant, which was a lower rate than for IDC (67.3%) and ILC (80.6%). In contrast to RFI, RFS events were driven more by non-breast cancer deaths in older patients. Significant prognostic factors for RFI among PMBC included positive lymph node(s) (HR, 2.42; 95% CI, 1.08-5.40), radiotherapy (HR, 0.44; 95% CI, 0.23-0.85), and endocrine therapy (HR, 0.25; 95% CI, 0.09-0.70). No differential chemotherapy associations with outcomes were detected across PMBC subgroups by nodal stage, tumor size, and age. A separate SEER database analysis also did not find any association of improved survival with adjuvant chemotherapy in these subgroups. Compared with IDC, PMBC demonstrated superior RFI, RFS, and OS. Lymph node negativity, adjuvant radiotherapy, and endocrine therapy were associated with superior RFI. Adjuvant chemotherapy was not associated with better outcomes.

Optimizing abemaciclib-induced diarrhea management in patients with breast cancer: a pragmatic 2-group study using a postbiotic microbiota stabilizer.

Abemaciclib-induced diarrhea is a relevant concern in clinical practice. Postbiotics have emerged as a promising option for managing it. We conducted a retrospective-prospective, 2-group, observational study to assess the impact of the postbiotic PostbiotiX-Restore, derived by Lactobacillus paracasei CNCM I-5220, on abemaciclib-induced diarrhea in patients with hormone receptor-positive HER2-negative breast cancer. The prospective population (Postbio group) received postbiotic during the first cycle of abemaciclib, while the retrospective one received standard care (Standard group). Diarrhea grading was defined according to the National Cancer Institute's Common Terminology Criteria for Adverse Events. During the first cycle, diarrhea occurred in 78.9% of patients in the Standard cohort and 97.1% in the Postbio one, with most cases being G1-G2. Severe (G3) diarrhea was significantly less frequent in the Postbio group (0%) compared to the Standard one (7.9%; P = .029). Over the entire study period, while the grading difference was not statistically significant, G3 events were less frequent in the Postbio population (5.9%) than the Standard one (15.4%). Moreover, Postbio patients required fewer dose reductions due to diarrhea compared to the Standard group (P = .002). Notably, in the Postbio population, G1 and G2 events had short median durations (3 and 1 days, respectively) and, for the 2 patients experiencing G3 events during the second abemaciclib cycle (off postbiotic), diarrhea lasted only 1 day. Our study demonstrates the effect of PostbiotiX-Restore in mitigating abemaciclib-induced diarrhea, resulting in reduced severity, fewer dose reductions, and shorter duration. Further exploration and validation in larger cohorts are needed.

Long-term prospective outcome data using EndoPredict as risk stratification and chemotherapy decision biomarker in hormone receptor-positive, HER2-negative early breast cancer

PurposeTo report the prospective long-term outcome data of patients whose chemotherapy decision was guided by the EndoPredict test.MethodsPatients with hormone receptor-positive HER2-negative early breast cancer with 0–3 positive lymph nodes were enrolled. The EndoPredict test was carried out on all tumor samples. Treatment compliance, local recurrence, distant metastases, and survival were evaluated. Associations of EPclin risk stratification with 5-year disease-free survival and distant metastasis-free survival were evaluated by time-to-event analysis.Results368 consecutive patients were included in the analysis. Median follow-up was 8.2 years. EndoPredict allocated 238 (65%) in the low-risk and 130 (35%) patients in the high-risk group. Risk for disease recurrence or death in EPclin high-risk patients was twofold higher than in EPclin low-risk patients (hazard ratio [HR] 2.08; 95% CI 1.26–3.44; p = 0.004). EPclin low-risk patients had a 5-year disease-free survival of 95.3% (95% CI 92.6–98.0%). EPclin high-risk patients were at higher risk of developing distant metastases or death (HR 2.21; 95% CI 1.27–3.88; p = 0.005). EPclin high-risk patients who underwent chemotherapy had a 5-year DFS of 89.1% (95% CI 82.7–96.1%) in contrast to high-risk patients without chemotherapy (68.9%; 95% CI 56.2–84.5%; HR 0.46; 95% CI 0.23–0.95; p = 0.036). EPclin high-risk patients were at higher risk of experiencing distant metastases or death than EPclin low-risk patients regardless of menopausal status (premenopausal: HR 3.55; 95% CI 1.17–12.32; p = 0.025; postmenopausal: HR 1.92; 95% CI 0.99–3.7; p = 0.054).ConclusionEndoPredict can guide decisions on adjuvant chemotherapy in early luminal breast cancer. EndoPredict risk stratification is also applicable in premenopausal women.

Abstract PO3-08-05: Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes

Abstract Background: Special histologic subtypes of breast cancer, including mucinous and tubular, account for 25% of all invasive breast cancers. Multigene tests (MGT) play a crucial role in guiding adjuvant chemotherapy and predicting prognosis for the patients with Hormone receptor-positive HER2-negative breast cancer. This research aims to examine the results of multigene tests for special histologic subtype patients and review the prognosis of each group. Methods: A retrospective analysis was conducted on data from 133 patients with special histologic subtypes of breast cancer who underwent surgery at Severance Hospital between November 2013 and December 2022. Each patient underwent one type of MGT, including Oncotype Dx, MammaPrint, or EndoPredict. Patients were grouped in two groups according to histologic types, based on WHO classification. Favorable types consist of type A mucinous carcinoma, pure tubular carcinoma, invasive solid papillary carcinoma, encapsulated papillary carcinoma with invasion, invasive cribriform carcinoma, secretory carcinoma, and invasive carcinoma with apocrine differentiation. Unfavorable types included type B mucinous carcinoma, mucinous carcinoma with micropapillary feature or neuroendocrine differentiation, mixed IDC, ILC or invasive micropapillary carcinoma, mixed invasive solid papillary carcinoma, mixed invasive papillary carcinoma, and mixed invasive cribriform carcinoma with IDC. Results: Patients with favorable types accounted for 42.86% (57 patients), while patients with unfavorable types accounted for 57.14% (76 patients). Patients with unfavorable histologic subtypes of breast cancer tended to have a higher incidence of high-risk results in MGT, as well as a greater prevalence of multiple (multifocal, multicentric) cancer and higher histologic grade. In multivariate analysis using logistic regression, unfavorable types showed a significantly high ratio of having high risk on MGT compared to the favorable type (OR = 4.327, 95% CI 1.210 – 15.475, p-value = 0.024). Moreover, overall survival in unfavorable histologic types showed a statistically significant difference between high-risk and low-risk in Kaplan-Meier survival analysis (p-value = 0.001). Conclusions: Unfavorable subtypes have shown a significantly higher-risk result of MGT, and patients with unfavorable types of breast cancer and high-risk MGT results have exhibited the worst prognosis. Consequently, we can suggest that MGT can be used as a prognosis evaluation tool for certain special subtypes of breast cancer and further utilized to aid in treatment decisions. Citation Format: Seung Hye Yang, Jee Hyun Ahn, Suk Jun Lee, Jee Ye Kim, Hyung Seok Park, Seung Il Kim, Byeong Woo Park, Seho Park. Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes [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 PO3-08-05.

Abstract PO3-28-06: YAP1 expression is a good prognostic marker of hormone receptor-positive HER2-negative breast cancer: clinicopathologic analysis using the 21-gene recurrent score

Abstract Background: YAP1 is a downstream transcription factor of Hippo pathway and considered an oncogene in numerous solid cancers. Oncotype Dx (ODX) test is a multigene test for patients with hormone receptor-positive, HER2-negative (HR+HER2-) breast cancer that provides a risk score (RS), a high RS means high-risk. In this study, we investigated the relation between YAP1 expression and RS in patients with HR+HER2- breast cancer and validated the clinical impact of YAP1 on breast cancer using public datasets. Methods: This retrospective study included 401 patients who received curative-purpose resection of HR+HER2- breast cancer and underwent ODX test between May 2014 and April 2020 at Gangnam Severance Hospital in Seoul, Korea. YAP1 nuclear localization was evaluated using immunohistochemical staining, and clinicopathological parameters including RS were analyzed. Clinical outcome was validated using YAP1 mRNA expression in TCGA-BRCA and METABRIC datasets. Results: High-YAP1 expression was significantly correlated with low ODX RS (OR [odds ratio] 0.373, 95% CI [confidence interval] 0.198-0.703, p=0.002). High expression of YAP1 mRNA correlated with superior clinical outcomes, particularly in patients with ER-positive breast cancer (p < 0.0001, overall survival [OS] in METABRIC; p=0.00085, recurrent-free survival [RFS] in METABRIC; p=0.040, disease-free survival [DFS] in TCGA-BRCA). With different ESR1 mRNA expression thresholds and highly expressed YAP1, patients in the upper 80-, 60-, or 40 percentiles of ESR1 expression levels consistently demonstrated superior OS and RFS in METABRIC as well as DFS in TCGA-BRCA. Conclusion: YAP1 could serve as a prognostic marker as well as a therapeutic target in patients with HR+HER2- breast cancer. Citation Format: Inho Park, Yangkyu Lee, Jee Hung Kim, Soong June Bae, Sung Gwe Ahn, Joon Jeong, Yoon Jin Cha. YAP1 expression is a good prognostic marker of hormone receptor-positive HER2-negative breast cancer: clinicopathologic analysis using the 21-gene recurrent score [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 PO3-28-06.

Abstract PO1-17-11: Trends in post-mastectomy reconstruction by age in Korea and among Asian-Americans

Abstract Background: Post-mastectomy immediate breast reconstruction (PMIBR) has been underutilized in the elderly. This study examines the trends of PMIBR by age in a large Korean medical center and compares them to the Asian-American population in the National Cancer Database (NCDB). Methods: We analyzed 5,601 patients who underwent PMIBR out of 13,654 total mastectomy patients between 2001 and 2021 in a Korean Center. Patient characteristics associated with higher likelihood of receiving reconstruction were assessed and compared between patients under 60 years of age and those aged 60 years and older. Complications were investigated in 1,669 patients between 2010 and 2020. In addition, we compared this to 966,354 female patients in the NCDB from 2004-2020 with stage 0-3 breast cancer who underwent mastectomy. Results: The number of PMIBR at the Korean center increased almost ten-fold, but there was a discrepancy in the increase between younger and older women. In the younger group, the proportion of PMIBR rose from 13% (53/398) to 77% (508/664), while in the older group, it increased from 0% (0/60) to 26% (49/186). In the NCDB, Asian-Americans had the lowest rate of breast reconstruction (29%) compared to white (35.4%), black (30.1%), and Hispanic Americans (33.5%). As seen in the table, the rates increased in both age groups but plateaued around 2014 and remained stable until 2020. In 2020, the PMIBR rates were 37% for young Asian-Americans, 48% for young non-Asians, 14% for older Asian-Americans, and 24% for older non-Asians. At the Korean center, patients living in a metropolitan area (42.6% vs.39.8% p=0.001), having higher education (44.7% vs. 10.5% p< 0.001), being unmarried (63.1% vs. 39.3% p< 0.001), having no history of childbirth (53.7% vs 39.9% p< 0.001), having lower stage and hormone receptor-positive HER2-negative breast cancer were more likely to undergo reconstruction. These factors were all more common in the younger age group. In the NCDB, patients receiving PMIBR were more likely to be white or non-Asian, have higher income and education, reside in a metropolitan area and in the Northeast, have less comorbidities, be treated in an academic center, and have a luminal subtype, lower stage, and private health insurance. At the Korean center, autologous reconstruction was more common than implant reconstruction, (68.4% vs. 31.6% for younger women, and 63.3% vs. 36.9% for older women) and the complication rate was similar for both age groups. In contrast, in the NCDB, implant reconstruction was more common in both age groups, tissue-based (29% vs 31%), implant-based (40.7% vs 40%), combined (11% vs 10.8%) and other (18% vs 17.6%) for older and younger women respectively. Conclusion: Both the Korean and American data illustrate remarkably lower utilization of immediate breast reconstruction in older patients. There are notable demographic and clinical differences between age groups but negligible difference in complication rates. Further research and interventions to address barriers in older women are needed. The higher rates of PMIBR in South Korea mirrors that of white women in the northeast USA, suggesting a potential disparity for Asian-Americans. Percentage of PMIBR over total mastectomy (with or without reconstruction) by age and race PMIBR= post-mastecomy immediate breast reconstruction; NCDB= national cancer database Citation Format: Soo-Young Lee, Madhav KC, Hyun Ho Han, Leah Kim, Mehra Golshan, Eric Schneider, Rachel Greenup, Donald Lannin, Hyung Bae Kim, Byung Ho Son, Jong Won Lee, Sae Byul Lee, Hee Jeong Kim, Tristen Park. Trends in post-mastectomy reconstruction by age in Korea and among Asian-Americans [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 PO1-17-11.

Abstract PO4-15-10: HER2-low Status among Patients with Li-Fraumeni Syndrome and Breast Cancer

Abstract Background: The HER2-low status has gained significance as a target for HER2-directed antibody drug conjugates in breast cancer. It is observed in approximately 60% of hormone receptor-positive (HR+) tumors and 30% of hormone receptor-negative (HR-) tumors. Some studies suggest that the HER2-low status by itself does not influence tumor biology or prognosis. Breast cancer in the context of Li-Fraumeni (LFS) syndrome has been characterized by an enrichment in HER2-positive (HER2+, defined as +3 in the immunohistochemistry [IHQ] or +2 in the IHQ with positive in situ hybridization [ISH]) disease. Considering this, we aimed to evaluate whether LFS patients with breast cancer also exhibit a higher frequency of HER2-low status. Methods: This retrospective-prospective cohort study included patients diagnosed with breast cancer who had a pathogenic/likely pathogenic TP53 germline variant and were treated at two cancer institutions between 1999 and 2023. The primary objectives were to determine the overall proportion of HER2-low status and its distribution according to hormone receptor status. HER2-low was defined as IHQ +1 or IHQ +2 with negative ISH. Results: Fifty-three patients (52 female and 1 male) were included in the study. The most common germline TP53 variant was the TP53 R337H (71.7%). The median age at breast cancer diagnosis was 39 years (range 21–62). The majority of patients had breast cancer of no special type (79%) or lobular carcinoma (11.3%), grade 2 (54.7%) or grade 3 (24.5%), and stage I-II (67.9%). Breast cancer subtypes would classically be classified as HER2+ in 34%, HR+HER2- in 58.5%, and triple-negative breast cancer (TNBC) in 7.5% of the patients. Biopsy samples were obtained from the primary tumor in 96.3% of the cases and from lymph nodes in 3.7%. Overall, 15.1% of the cases exhibited HER2-low status, 34% were HER2-negative, and 17% were HER2-negative without IHC details (Table). In a hypothetical scenario assuming all cases without IHC details were HER2-low, the maximum estimated frequency of HER2-low status would be 32.1%. Among HR+ patients, 25.8% had HER2-low status, 45.2% were HER2-negative, and 29% were HER2-negative without IHC details. All four patients with TNBC exhibited HER2-zero status. Conclusion: Contrary to our initial hypothesis, the frequency of HER2-low status in this cohort of LFS patients with breast cancer was lower than anticipated. These results suggest that while breast cancer developing in the context of germline TP53 variants appears to be associated with HER2 amplification, it does not impact lower expressions of HER2. This observation reinforces the concept that HER2-low status does not seem to play a significant role as a driver of tumorigenesis. Further expansion of the study cohort and pathology analysis is planned to confirm these findings. Table HER2 status overall and according to hormone receptor-status (for HER2-negative patients). Abbreviations: IHQ, immunohistochemistry; HR+HER2- BC, hormone receptor-positive HER2-negative breast cancer; TNBC, triple-negative breast cancer. Citation Format: Luciana Auresco, Renata Colombo Bonadio, Vanessa Petry, Laura Testa, Camila Moniz, Jennifer Dos Santos, Maria Del Pilar Estevez-Diz, Rodrigo Santa Cruz Guindalini. HER2-low Status among Patients with Li-Fraumeni Syndrome and 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 PO4-15-10.

Abstract GS03-07: Protocol-defined biomarker analysis in the PALLAS (AFT-05) adjuvant trial: Genomic subtype derived from RNA sequencing of HR+/HER2- early breast cancer

Abstract Background. The phase 3 PALLAS trial (NCT02513394) compared two years of the CDK4/6 inhibitor palbociclib with endocrine therapy of provider choice, versus endocrine therapy alone, as adjuvant treatment for patients with Stage II-III hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer. Genomic subtype (PAM50 intrinsic subtype) measured from whole-transcriptome RNA sequencing data was defined in the protocol of the PALLAS trial as the primary biomarker for analysis of prediction and prognosis. Clinical data have been previously presented (Gnant et al, JCO 2022), and the trial now has 5-year median follow-up. Methods. As part of trial eligibility, all participants in PALLAS provided a tumor tissue block prior to randomization (surgical if primary resection, core biopsy if neoadjuvant treatment) for translational analyses (TRANS-PALLAS). The biorepository and laboratory were blinded to identity and processed samples in random order, to minimize bias. Nucleic acids were extracted from samples with sufficient tumor tissue and cellularity (>25 mm2 with ≥20% cancer nuclei). The Genome Sequencing Center at Washington University St. Louis performed whole-transcriptome RNA sequencing. Libraries were prepared from 1 µg DNase-1 treated total RNA, if total RNA DV200 >28 (Agilent Bioanalyzer), using an unbiased library protocol of RNA HyperPrep kit with RiboErase (HMR) (Kapa Biosystems, Wilmington, MA). 100 bp paired-end sequencing was performed on NovaSeq 6000 using S4 Reagent Kit (Illumina, San Diego, CA), with 48 libraries pooled per lane. Intrinsic subtype was determined using Bioclassifier package (Research PAM50 script, Parker et al.) only for the analysis population of primary breast cancer samples that had not been exposed to prior neoadjuvant therapy. Invasive disease-free survival (IDFS) will be visualized using Kaplan-Meier plots, with log-rank test between groups. Cox models of proportional hazards will be developed to evaluate prognosis adjusted for known clinical covariates, or for predictive interactions. The pre-defined level of significance is a two-sided 0.05. Results. From the total study population of 5796 enrolled patients, 4655 tissue blocks had sufficient tumor content to process for RNA, with 3931 yielding sufficient RNA for sequencing, and 2669/4655 (57.3%) submitted tissue blocks had DV200 ≥28 and were successfully sequenced. Clinical unblinding revealed 2370 unique patients (1182 in the palbociclib treatment arm and 1188 in the control arm) with intrinsic subtype defined from their untreated primary tumor: 1555 (65.6%) luminal A, 287 (12.1%) luminal B, 167 (7.0%) HER2-enriched, 310 (13.1%) basal-like, 51 (2.2%) normal-like. We will report the results for association of molecular subtype, proliferation score, and Risk of Recurrence (ROR) scores with invasive disease-free survival (IDFS) by treatment arm at the meeting. Conclusions. The TRANS-PALLAS cohort represents one of the largest biorepositories of HR+/HER2- early breast cancer reflecting contemporary systemic management in the framework of a prospectively randomized global trial. Required tumor block submission in this phase 3 trial yielded data from unbiased whole-transcriptome RNA sequencing of the primary tumor prior to treatment from 41% of the PALLAS participants. The proportion of luminal A cancers was unexpectedly high (66%), indicating a lower-risk distribution of cancers in this population. The planned analyses of prediction and prognosis are ongoing and those results will be presented at the time of the meeting. Support: AFT, ABCSG, Pfizer, ECOG-ACRIN, NSABP Foundation, GBG, BIG; Clinicaltrials.gov Identifier: NCT02513394; https://acknowledgments.alliancefound.org Citation Format: Daniel Stover, Dominik Hlauschek, Erica Mayer, W. Fraser Symmans, Mark Watson, Iros Barozzi, Martin Filipits, Karla Ballman, Meritxell Bellet- Ezquerra, Justin Balko, Gabor Rubovszky, Nicholas Zdenkowski, Adam Brufsky, Guenther Steger, Claudine Isaacs, Sibylle Loibl, Fernando Henao, Meredith Regan, Yuan Liu, Christian Fesl, Patrick O'Brien, Angela DeMichele, Michael Gnant, Otto Metzger. Protocol-defined biomarker analysis in the PALLAS (AFT-05) adjuvant trial: Genomic subtype derived from RNA sequencing of HR+/HER2- early 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 GS03-07.

Abstract PO1-04-12: Palbociclib versus ribociclib in first-line treatment of patients with hormone-receptor positive HER2 negative advanced breast cancer – real world outcome data from the German registry platform OPAL

Abstract Introduction CDK4/6 inhibitors (CDKi) plus endocrine therapy (ET) are standard of care in first-line (1L) treatment of hormone receptor-positive (HR+) HER2-negative (HER2-) advanced breast cancer (ABC). In the pivotal trials the three CDK4/6i (palbociclib, ribociclib and abemaciclib) + ET showed similar progression-free survival (PFS) benefit over ET alone. However, other than ribociclib, palbociclib failed to demonstrate overall survival (OS) benefit. As patient (pts) characteristics differed between the trials, especially in the number of pts with treatment-free interval (TFI) of < 12 months after end of adjuvant ET, head-to-head comparisons of the CDKi are of clinical interest. Here we analyze the outcome of pts treated with palbociclib + ET or ribociclib + ET with real-world data from OPAL. Methods OPAL (NCT03417115) is a prospective observational, open, longitudinal multicenter cohort study (clinical registry) in Germany. Pts with ABC and early breast cancer can be recruited at start of their first systemic treatment. There are no treatment restrictions. Sites from all medical sectors can participate in OPAL (medical and gynecologic oncologists from outpatient centers and hospitals). Details on all (sequential) treatments, patient and tumor characteristics, biomarker testing, clinical and patient-reported outcomes are collected. Follow-Up is until death or up to 5 years. Between 01/2018 and 07/2021 1049 pts with HR+ HER2- ABC were recruited by 143 sites. Database cut was on 31/08/2022. 384 pts received palbociclib + ET and 231 pts received ribociclib + ET as 1L treatment. All endocrine combination partners including switch of ET during first line therapy was allowed, whereas switch of CDK4/6i (n=25) were excluded. PFS in registries can differ from PFS in clinical trials, since the RECIST criteria are usually not applied in routine care. PFS in registries represents the time to clinically relevant progression in routine care. PFS and OS were estimated using the Kaplan-Meier method. To adjust for confounding, inverse probability of treatment weighting (IPTW) by propensity score analysis was used to compare PFS and OS between 1L palbociclib+ET and ribociclib+ET. IPTW was performed for the following variables: age, menopausal status, ECOG, any comorbidity, Charlson comorbidity index, metastatic stage, type of metastasis, number of metastatic sites, estrogen-/progesterone status, IHC status, previous chemo-/endocrine therapy, kind of endocrine combination partner, disease-free interval, and treatment-free interval. Results From 2018 to 2021, the proportion of CDK4/6i increased from 68% to 86% in 1L of HR+HER2- ABC. Overall, palbociclib was used in 44% and ribociclib in 26% of all first-line treatments in OPAL. Median age of pts receiving palbociclib/ribociclib was 66/68 years and for 77/81% of pts at least one comorbidity was documented. 37/35% of pts already had metastasis at diagnosis (M1) and 25/26% of pts had a TFI < 12 months. After IPTW, the two treatment groups were comparable for all tested characteristics. 42/46% of patients had a progression (palbociclib/ribociclib group). IPTW-adjusted median PFS was 25.1 months (95% Confidence interval (CI) 20.1 – 30.1) for the palbociclib and 27.0 months (95%-CI 21.1 – 31.6) for the ribociclib group. Hazard ratio was 0.91 (0.71 – 1.17) for palbociclib versus ribociclib. 26/29% of patients had an OS event (palbociclib/ribociclib group). IPTW-adjusted median OS was 36.7 months (95%-CI 33.0 – NA) for the palbociclib and 36.6 months (95%-CI 33.1 – NA) for the ribociclib group. Hazard ratio was 0.95 (0.69 - 1.30) for palbociclib versus ribociclib. Conclusions This analysis of real word data in the OPAL registry platform showed similar PFS and OS for palbociclib + ET compared to ribociclib + ET, when adjusted for a wide range of potential confounding variables. Further analyses will investigate whether one drug showed favorable results in certain subgroups of pts. Citation Format: Marc Thill, Mark-Oliver Zahn, Anja Welt, Arnd Nusch, Matthias Zaiss, Kathrin Engelken, Gabriele Kaltenecker, Kai Ringwald, Katja Gratzke, Lisa Kruggel, Martina Jänicke, Holger Schulz, Christoph Losem, Volker Hagen, Roland Fricker, Elmar Stickeler, Nadia Harbeck, Achim Wöckel, Thomas Decker. Palbociclib versus ribociclib in first-line treatment of patients with hormone-receptor positive HER2 negative advanced breast cancer – real world outcome data from the German registry platform OPAL [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 PO1-04-12.

Calcification-associated molecular traits and therapeutic strategies in hormone receptor-positive HER2-negative breast cancer.

Mammographic calcifications are a common feature of breast cancer, but their molecular characteristics and treatment implications in hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer remain unclear. We retrospectively collected mammography records of an HR+/HER2- breast cancer cohort (n = 316) with matched clinicopathological, genomic, transcriptomic, and metabolomic data. On the basis of mammographic images, we grouped tumors by calcification status into calcification-negative tumors, tumors with probably benign calcifications, tumors with calcification of low-moderate suspicion for maligancy and tumors with calcification of high suspicion for maligancy. We then explored the molecular characteristics associated with each calcification status across multiple dimensions. Among the different statuses, tumors with probably benign calcifications exhibited elevated hormone receptor immunohistochemical staining scores, estrogen receptor (ER) pathway activation, lipid metabolism, and sensitivity to endocrine therapy. Tumors with calcifications of high suspicion for malignancy had relatively larger tumor sizes, elevated lymph node metastasis incidence, Ki-67 staining scores, genomic instability, cell cycle pathway activation, and may benefit from cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors. Our research established links between tumor calcifications and molecular features, thus proposing potential precision treatment strategies for HR+/HER2- breast cancer.

Abstract 1535: Differential immune microenvironments in triple-negative breast cancer and hormone receptor-positive HER2-negative breast cancer: A spatial analysis via multiplex immunofluorescence

Abstract Objective: To elucidate differences in immune cell (IC) composition and their spatial distribution between triple-negative breast cancer (TNBC) and hormone receptor-positive HER2-negative breast cancer (HR+HER2-BC), and to evaluate the effect of PD-L1 status on these parameters. Methods: We selected 32 patients with ≥60% tumor-infiltrating lymphocytes (TIL) (TNBC, n=18; HR+HER2- BC, n=14). Multiplex immunofluorescence was employed on resected tumor tissues. Using markers such as CK, CD20, CD8, CD4, and FOXP3, IC types and tumor cells (TC) were identified in both stromal and tumor areas. We analyzed and compared cellular density and proportional distribution of IC, and spatial interactions (both IC-TC and IC-IC) based on tumor subtype and PD-L1 status. Results: TNBC exhibited a unique IC composition with a higher proportion of CD8+IC (stroma: 27% vs 17%, p<0.001; tumor: 54% vs 31%, p<0.001) and CD4+FOXP3+IC (stroma: 3.9% vs 3.0%, p=0.036) than HR+HER2-BC. Among PD-L1 positive cases, TNBC had a denser stromal population of CD4+FOXP3+IC (146.4±67.1/mm2 vs 114.3±146.9/mm2, p=0.036). Both tumor subtypes displayed varied IC compositions based on PD-L1 status. Density plots revealed a pronounced clustering of IC near TC in TNBC, especially in PD-L1 positive cases. Analysis of cell-cell interactions showed diverse adjacency patterns between TC and various IC combinations with frequencies differing by tumor subtype and PD-L1 status. Conclusion: The immune landscape, typified by IC composition and spatial distribution, varies between TNBC and HR+HER2- BC, with PD-L1 status further modulating these patterns. Citation Format: Yoon Jin Cha, Inho Park, Su-Jin Shin. Differential immune microenvironments in triple-negative breast cancer and hormone receptor-positive HER2-negative breast cancer: A spatial analysis via multiplex immunofluorescence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1535.

Elderly patients with hormone receptor-positive HER2-negative metastatic breast cancer treated with CDK4/6 inhibitors in a multicentre cohort

IntroductionCyclin-dependent kinases 4/6 inhibitors (CDK 4/6i) combined with endocrine therapy have become the gold standard in hormone receptor-positive (HR +) HER2-negative (HER2-) metastatic breast cancer (MBC). However, there is a significant lack of data regarding the efficacy and safety of these treatments in elderly patients. We present the results of a real-world data (RWD) cohort stratified by age at treatment initiation (≥ 70 years compared to patients < 70 years).MethodsClinico-pathological data of HR + HER2- MBC patients who were candidates for CDK4/6i therapy between January 2017 and December 2020 at the Institut Català d'Oncologia (Spain) were retrospectively collected. The primary goal was to assess Progression-Free Survival (PFS), Overall Survival (OS), and safety outcomes within this patient population.ResultsA total of 274 patients with MBC who received CDK4/6i treatment were included in the study. Among them, 84 patients (30.8%) were aged ≥ 70 years, with a mean age of 75, while 190 patients (69.2%) were under the age of 70, with a mean age of 55.7 years. The most frequently observed grade 3–4 toxicity was neutropenia, with similar rates in both the < 70 group (43.9%) and the ≥ 70 group (47.9%) (p = 0.728). The median Progression-Free Survival (mPFS) for the first-line CDK4/6i treatment was 22 months (95% CI, 15.4–39.8) in the < 70 group and 20.8 months (95% CI 11.2–NR) in the ≥ 70 group (p = 0.67). Similarly, the median PFS for the second-line CDK4/6i treatment was 10.4 months (95% CI, 7.4–15.1) and 7.1 months (95% CI 4.4–21.3) (p = 0.79), respectively. Median overall survival (mOS) was not reached either for the first- and second-line treatment.ConclusionsOur RWD suggests that elderly patients, when compared to those under 70, experience similar survival outcomes and exhibit comparable tolerance for CDK4/6i therapy.

CDK4/6i-treated HR+/HER2- breast cancer tumors show higher ESR1 mutation prevalence and more altered genomic landscape

As CDK4/6 inhibitor (CDK4/6i) approval changed treatment strategies for patients with hormone receptor-positive HER2-negative (HR+/HER2-) breast cancer (BC), understanding how exposure to CDK4/6i affects the tumor genomic landscape is critical for precision oncology. Using real-world data (RWD) with tumor genomic profiling from 5910 patients with metastatic HR+/HER2- BC, we investigated the evolution of alteration prevalence in commonly mutated genes across patient journeys. We found that ESR1 is more often altered in tumors exposed to at least 1 year of adjuvant endocrine therapy, contrasting with TP53 alterations. We observed a similar trend after first-line treatments in the advanced setting, but strikingly exposure to aromatase inhibitors (AI) combined with CDK4/6i led to significantly higher ESR1 alteration prevalence compared to AI alone, independent of treatment duration. Further, CDK4/6i exposure was associated with higher occurrence of concomitant alterations in multiple oncogenic pathways. Differences based on CDK4/6i exposure were confirmed in samples collected after 2L and validated in samples from the acelERA BC clinical trial. In conclusion, our work uncovers opportunities for further treatment personalization and stresses the need for effective combination treatments to address the altered tumor genomic landscape following AI+CDK4/6i exposure. Further, we demonstrated the potential of RWD for refining patient treatment strategy and guiding clinical trial design.

415P Patterns of time-to-progression intervals across clinical and liquid biopsy (LB) features in hormone receptor-positive (HR+) HER2-negative (HER2-) metastatic breast cancer (MBC) patients (pts) treated with first-line endocrine therapy (ET)

415P Patterns of time-to-progression intervals across clinical and liquid biopsy (LB) features in hormone receptor-positive (HR+) HER2-negative (HER2-) metastatic breast cancer (MBC) patients (pts) treated with first-line endocrine therapy (ET)

HORMON RESEPTÖR POZİTİF, HER-2 NEGATİF METASTATİK MEME KANSERLİ HASTALARDA CDK4/6 İNHİBİTÖRÜ TEDAVİSİ ÖNCESİ SİSTEMİK İMMÜN İNFLAMASYON İNDEKSLERİNİN VE PROGNOSTİK NUTRİSYONEL İNDEKSİN PROGNOSTİK ÖNEMİ

Abstract&#x0D; Purpose: As systemic inflammatory indices and prognostic nutritional index are associated with poor prognosis in many tumor types, the goal of the present study was to ascertain their effect along with the neutrophil/lymphocyte ratio, platelet/lymphocyte ratio, lymphocyte/monocyte ratio, C-reactive protein/albumin ratio, and systemic inflammatory response index on the progression-free survival (PFS) and overall survival (OS) of hormone receptor-positive HER2-negative (HR+/HER2−) metastatic breast cancer patients before CDK4/6 inhibitor treatment. &#x0D; Materials and Method: The medical records of 79 patients with HR+/HER2− metastatic breast cancer who presented at the Medical Oncology Outpatient Clinic between January 2018 and May 2022 were retrospectively analyzed to gather relevant data measured before CDK4/6 inhibitor treatment in order to establish the effect of key markers on their PFS and OS.&#x0D; Results: The median age of the participating patients, 70 (88.6%) of whom were postmenopausal, was 53 years (range 26−80 years). While 68 patients (86.1%) had a 0 performance score, 10 (12.7%) developed metastases during adjuvant endocrine therapy. Factors affecting PFS were age