Predictors of prolonged benefit from palbociclib plus fulvestrant in women with endocrine-resistant hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer in PALOMA-3.

•PALOMA-3 extended follow-up confirms progression-free survival improvement with palbociclib-fulvestrant.•With palbociclib-fulvestrant, 29% of patients had a benefit for ≥18 months.•Only 15% of patients receiving placebo-fulvestrant had prolonged clinical benefit.•Long-term responders in both arms had less disease burden and fewer prior therapies.•No prognostic factors of prolonged benefit were identified for the palbociclib arm.