Independent validation of the PAM50-based chemo-endocrine score (CES) in hormone receptor-positive HER2-positive breast cancer treated with neoadjuvant anti-HER2-based therapy

Purpose: We do not yet have validated biomarkers to predict response and outcome within hormone receptor-positive/HER2-positive (HR+/HER2+) breast cancer. The PAM50-based chemoendocrine score (CES) predicts chemo-endocrine sensitivity in hormone receptor-positive/HER2-negative (HR+/HER2-) breast cancer. Here, we evaluate the relationship of CES with response and survival in HRþ/HER2þ breast cancer. Experimental Design: Intrinsic subtype and clinicopathologic data were obtained from seven studies in which patients were treated with HER2-targeted therapy either with endocrine therapy (ET) or with chemotherapy (CTX). CES was evaluated as a continuous variable and categorically from low to high scores [CES-C (chemo-sensitive), CES-U (uncertain), and CES-E (endocrine-sensitive)]. We first analyzed each dataset individually, and then all combined. Multivariable analyses were used to test CES association with pathologic complete response (pCR) and disease-free survival (DFS). Results: A total of 457 patients were included (112 with ET and 345 with CTX). In the combined cohort, CES-C, CES-U, and CES-E were identified in 60%, 23%, and 17% of the patients, respectively. High CES (i.e., CES-E) was associated with a lower probability of achieving pCR independently of clinical characteristics, therapy, intrinsic subtype, and study (adjusted OR ¼ 0.42; P ¼ 0.016). A total of 295 patients were analyzed for DFS with a median follow-up of 66 months. High CES was also associated with better DFS (adjusted HR, 0.174; P ¼ 0.003) independently of pCR, clinical characteristics and intrinsic subtype. In patients with residual disease, the adjusted DFS HR of CES was 0.160 (P ¼ 0.012). Conclusions: In HER2þ/HRþ breast cancer, CES is useful for predicting chemo-endocrine sensitivity and provides additional prognostication beyond intrinsic subtype and clinicopathologic characteristics.