Background: 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 > 2 y (26–39 cycles). In contrast, 38/174 (22%) pts on P+F received ≥12 mo of tx; only 16 (9%) received > 2 y (27–38 cycles). No apparent differences in baseline characteristics of pts with long-term benefit were observed between groups except that a greater proportion of those on P+F had a single site of disease involvement (40% PAL+F vs 63% P+F). Pts with long-term benefit on PAL+F had lower rates of visceral disease (42% vs 60%), liver metastases (18% vs 40%), and ≥3 disease sites (27% vs 39%) at baseline vs the ITT population; no difference in sensitivity to prior ET was observed (84% vs 79%). Objective response rate (ORR) was higher among pts with prolonged benefit on PAL+F vs ITT (36% vs 26%). Conclusions: PAL+F is associated with prolonged benefit in about a third of pts treated with the combination in PALOMA-3. These pts achieve higher ORR compared to other study pts and the benefit is independent of baseline site and number of metastatic recurrences and prior endocrine sensitivity. Benefit from F alone is less prolonged and appears limited to those with 1 site of disease involvement. The analysis confirms the efficacy of PAL+F in HR+ ABC with visceral recurrence. Biomarker analyses are ongoing in pts with long-term benefit to understand molecular features predictive of tx sensitivity. Funding: Pfizer. Clinical trial information: NCT01942135