Multinational phase 3 trial of addition of palbociclib to first-line standard therapy in HR-positive, HER2-negative metastatic breast cancer

Dual anti-HER2 therapy followed by maintenance treatment with HER2-targeted and endocrine therapies is standard first-line treatment for HR-positive, HER2-negative metastatic breast cancer (HR+ HER2- mBC). The CDK4/6 inhibitor palbociclib may overcome resistance to both endocrine and HER2-directed therapies. In the multinational phase 3 PATINA trial, patients with HR+ HER2- mBC who did not have disease progression after four to eight cycles of chemotherapy plus HER2-targeted therapy were randomized 1:1 to receive maintenance HER2-targeted and endocrine therapies with palbociclib (n=261) or without palbociclib (n=257). The primary endpoint was investigator-assessed progression-free survival (PFS). At a median follow-up of 53.5 months, the median PFS was 44.3 months in the palbociclib group and 29.1 months in the standard-therapy group (HR 0.75; p=0.02), with grade 3 and 4 adverse events occurring in 79.9% and 10.0%, respectively, of the patients in the palbociclib group as compared in 30.6% and 3.6%, respectively, of the patients in the standard-therapy group. The authors conclude that the addition of palbociclib to standard maintenance therapy led to a significant improvement in PFS, with increased toxic effects (quick take video summary).