Palbociclib and trastuzumab for HER2-positive metastatic breast cancer: final overall survival results of cohort A and B of SOLTI-1303-PATRICIA trial

The SOLTI-1303-PATRICIA trial (NCT02448420) is a phase II study investigating palbociclib and trastuzumab, with or without endocrine therapy, in hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC). This manuscript presents final overall survival (OS) results and biomarker analyses. Patients previously treated with trastuzumab and two to four regimens were eligible. For estrogen receptor (ER)-negative disease (cohort A), patients received palbociclib and trastuzumab. For ER-positive disease, patients were randomized 1 : 1 to cohort B1 (no additional therapy) or B2 (letrozole). OS and long-term progression-free survival (PFS) were pre-defined secondary endpoints. Kaplan-Meier curves and stratified Cox models were used. Among 71 patients, median OS was 29.8 months [95% confidence interval (CI) 20.9-38.0 months]; 4-year OS rates were 13.3% (A), 35.7% (B1), and 32.3% (B2). PAM50 luminal subtypes showed better OS than non-luminal subtypes (38.0 versus 26.6 months). Exploratory biomarker analyses found luminal-related genes associated with better long-term survival, while basal and proliferation-related genes were linked to resistance. Higher luminal A, luminal B, and previously reported chemo-endocrine scores correlated with favorable prognoses. These findings highlight the relevance of gene expression profiling in HER2-positive breast cancer and support biomarker-driven patient selection. Long-term PATRICIA results validate the potential of non-chemotherapy-based approaches in HR-positive/HER2-positive MBC.