Efficacy outcomes of CDK4/6 inhibitors in combination with endocrine therapy treatment in hormone receptor-positive/HER2-negative advanced breast cancer according to PAM50 intrinsic subtype: Primary results of SOLTI-1801 CDK-PREDICT study.

INTRODUCTION

The prognostic value of PAM50 intrinsic subtypes (IS), cell cycle, and immune-related gene expression in HR+ /HER2- advanced breast cancer (BC) treated with CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) in a first-line metastatic setting is unclear. This study evaluates these biomarkers in metastatic biopsies from patients diagnosed with HR+ /HER2- advanced BC.

METHODS

CDK-PREDICT study is a multicentric, ambispective observational cohort study conducted in six Spanish hospitals. It included patients diagnosed with HR+ /HER2- advanced BC treated in the first-line setting with CDK4/6i and ET. Baseline biopsies were obtained prior to treatment to determine research-based PAM50 IS, cell cycle and immune-related gene expression. The primary objective was to evaluate progression-free survival (PFS) differences among PAM50 IS using uni- and multivariable Cox regression models. Secondary objectives included overall survival (OS), overall response rate (ORR), and correlating cell cycle and immune response gene expression with PFS.

RESULTS

A total of 185 patients were included, with a median follow-up of 38.5 months. PAM50 luminal subtypes were predominant (82.7 %). Non-luminal subtypes showed significantly shorter median PFS (10.2 vs. 25.7 months; HR, 2.50; p < 0.001) and OS (32.3 vs. 58.1 months; HR, 2.54; p < 0.001) than luminal subtypes. Higher cell cycle and immune-related genes expression, such as CCNE1 and PDCD1, as well as tumor infiltrating lymphocytes were associated with poorer outcomes.

CONCLUSIONS

This study confirms the independent prognostic value of PAM50 IS in HR+ /HER2- advanced BC treated with CDK4/6i and ET. Non-luminal subtypes exhibited the worst prognosis, underscoring the need for novel therapeutic strategies in this population.