Predictors Of Prolonged Benefit From Palbociclib (Pal) Plus Fulvestrant (F) In Women With Endocrine Resistant Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative (Hrill-Ier2-) Advanced Breast Cancer (Abc) In Palo Ma-3.

1050Background: PAL+F improved progression-free survival (PFS) over F + placebo (P) in patients (pts) with endocrine-resistant HR+/HER2– ABC. We examined factors predictive of long-term benefit on PAL+F. Methods: Pre/postmenopausal pts with HR+/HER2– ABC that progressed on prior endocrine therapy (ET) were randomized 2:1 to PAL (125 mg/d oral [3 wk on, 1 wk off]) + F (500 mg) or P+F. Characteristics of pts with prolonged benefit (treatment [tx] duration ≥18 mo for PAL+F; ≥12 mo for P+F based on median PFS and tx duration) were compared with the intent-to-treat (ITT) population. Results: PAL+F improved PFS vs P+F (11.2 vs 4.6 mo; hazard ratio, 0.50). By Aug 2016, 138 pts had long-term benefit: 100/347 (29%) pts on PAL+F received tx for ≥18 mo, including 70 (20%) who received u003e 2 y (26–39 cycles). In contrast, 38/174 (22%) pts on P+F received ≥12 mo of tx; only 16 (9%) received u003e 2 y (27–38 cycles). No apparent differences in baseline characteristics of pts with long-term benefit were observed between group...