Prognostic value of PAM50 in residual breast cancer following neoadjuvant endocrine therapy (NET): A retrospective analysis with long follow-up.

Abstract

575 Background: NET is gaining more acceptances for the management of hormonal receptors (HR)-positive breast cancer (BC). To date, the decrease of Ki-67 and PEPI score are the only prognostic factors associated with relapse-free survival after NET. PAM50 is a validated prognostic test in newly diagnosed BC; however, its value in residual tumors after NET is currently unknown. Methods: We took tumor tissues from patients of a retrospective study of 119 postmenopausal women with HR-positive stage II-III BC. Patients were diagnosed from 1997 to 2009 and were treated with NET for a median duration of 8.5 months . Median age was 74 (63-88). After NET all patients underwent surgery (73% conservative). Adjuvant treatment were endocrine therapy in 100%, radiotherapy in 76.5% and chemotherapy 7%. Median follow-up from surgery was 112 months. Median follow-up from surgery was 112 months. We observed 26 (24%) of distant relapses and 75 deaths (44 without cancer). Median overall survival was 134.8 months. RNA was extracted from FFPE tumor tissues of surgical specimens. A panel of 55 BC-related genes, including the research-based PAM50 assay (subtypes, ROR-S and ROR-P pre-defined cutpoints), androgen receptor (AR), immune genes (CD8A, CD4, PDL1 and PD1). Uni- and multi-variable Cox models were used to evaluate the association of each variable with distance recurrence free interval (DRFI). Results: PAM50 subtype distribution: Luminal A 54.3%, Normal-like 24.3%; HER2-enriched 16,5%, Luminal B 1% and basal 1%. Distribution of ROR-S groups was Low 64%, medium 30%and high 6%. Distribution of PEPI score was: 0 in 43%, 3 in 37% and 6 in 20%. Among the different variables explored, PEPI score 0 (HR 0.27 [95%IC 0.09-0.79] p=0.001), low ROR-S (HR 0.39 [95%CI 0.17-0.91] p=0.001) and high AR expression (HR 0.71 [95CI 0.53-0.96] p=0.007) were significantly associated with lower DRFI in univariate analyses. After adjusting for PEPI (with or without Normal-like tumors), ROR-S and AR remained significantly associated with outcome. Conclusions: PAM50 ROR-S and AR expression in residual tumors after NET provide independent prognostic information beyond PEPI. With further validation, these biomarkers could help clinicians in the decision-making of adjuvant chemotherapy.