Impact of hormone receptor status and tumor subtypes on clinical behavior and outcomes of breast cancer in young BRCA carriers.

504 Background: Hormone receptor expression is a known positive prognostic and predictive factor in breast cancer (BC). Among young patients harboring germline BRCA1or BRCA2 (BRCA) pathogenic variants (PVs), most of the tumors arising in BRCA2carriers express hormone receptors, while most BC cases in BRCA1 carriers do not; however, limited evidence exists on the impact of hormone receptor status on clinical behavior and outcomes in young patients harboring BRCA PVs. Methods: This is an international, multicenter, hospital-based, retrospective cohort study including young patients (≤40 years) diagnosed with invasive BC between January 2000 and December 2020, harboring germline PVs in BRCA genes. Our analysis investigates the impact of hormone receptor status on clinical behavior and outcomes of BC. The type and pattern of recurrence and survival outcomes (disease-free survival [DFS], BC specific survival [BCSS] and overall survival [OS]) were first investigated according to hormone receptors expression (positive vs. negative), and then according to BC subtype (luminal A-like vs. luminal B-like vs. triple-negative vs. HER2-positive BC). Results: From 78 centers worldwide, 4,709 BRCA carriers were included in this analysis, of whom 2,143 (45.5%) had hormone receptor-positive and 2,566 (54.5%) hormone receptor-negative BC. Patients with hormone receptor-positive BC were more likely to harbor BRCA2 PVs while less frequently had grade 3 tumors and nodal involvement. Median follow-up was 7.88 (IQR 4.47-12.61) years. The rate of distant recurrences was higher in patients with hormone receptor-positive BC (13.1% vs. 9.6%, p<.001), while the rate of second primary BC was lower (9.1% vs. 14.7%, p<.001) when compared to patients with hormone receptor-negative disease. The 8-years DFS was 65.8% in patients with hormone receptor-positive and 63.4% in those with hormone receptor-negative BC. No differences in terms of OS nor BCSS were observed. The hazard ratio of hormone receptor-positive vs. negative disease changed over time for DFS, BCSS, and OS (p<.05 for interactions of hormone receptor status and survival time). Among the 4,363 patients eligible for subtypes analysis, 612 had luminal A-like, 1,038 luminal B-like, 2,373 triple-negative and 340 HER2-positive BC. Patients with Luminal A-like BC had the worst long-term prognosis in terms of DFS compared to all the other subgroups (8-years DFS: 60.8% in luminal A-like vs. 63.5% in triple-negative vs. 65.5% in HER2-positive and 69.7% in luminal B-like subtype). Conclusions: In young BRCAPVs carriers with early BC, hormone receptor status did not appear to be a positive prognostic factor. The differences in pattern of recurrence and second primary BC among hormone receptor-positive vs. negative disease warrants consideration in counseling patients on treatment, follow-up strategies and indication for risk-reducing surgery.