Patient-reported outcomes (PROs) in patients (pts) with PIK3CA-mutated hormone receptor-positive (HR+), human epidermal growth factor receptor-2–negative (HER2–) advanced breast cancer (ABC) from SOLAR-1.

1039 Background: Approximately 40% of pts with HR+, HER2– ABC have tumors with a PIK3CA mutation, resulting in phosphatidylinositol 3-kinase (PI3K) pathway hyperactivation. Use of the oral α-specific PI3K inhibitor alpelisib (ALP) + fulvestrant (FUL) in SOLAR-1 significantly improved (vs placebo [PBO] + FUL) both progression-free survival (PFS) (median 11.0 vs 5.7 mo, respectively; HR 0.65; 95% CI, 0.50-0.85; P< 0.001) and objective response rate (ORR) (measurable disease: 36% vs 16%; P< 0.001) in the PIK3CA mutant cohort. In addition to primary efficacy and safety measures, PROs offer valuable insight into therapeutic benefit by measuring whether quality of life (QoL) is maintained during treatment. Methods: Postmenopausal women or men with HR+, HER2– ABC whose disease progressed on/after an aromatase inhibitor were randomized to receive ALP 300 mg once daily or PBO, + FUL 500 mg every 28 days + Cycle 1, Day 15. Secondary objectives included PROs using the EORTC QLQ-C30, EQ-5D-5L, and BPI-SF scales. PROs were collected at screening, every 8 wk for 18 mo then every 12 wk thereafter, at end of treatment, and during follow-up for efficacy. Linear mixed effects models were used to assess score changes from baseline. Time to 10% deterioration (TTD), an established measure of clinically meaningful change in QoL, was compared between the treatment arms’ survival distribution using Kaplan-Meier methodology. Results: At baseline, 93% of pts in the PIK3CA mutant cohort (n = 341) completed questionnaires; ≥75% completed them post-baseline. Adjusted mean changes from baseline in EORTC global health status/QoL scores were < 10% for all visits through wk 96 for both arms, with a mean difference between arms of < 3% for all visits. There was no difference between arms in TTD in global health/QoL status (HR 1.03; 95% CI, 0.72-1.48). Analysis of TTD in EORTC physical, social, and emotional functioning scores revealed no meaningful differences between arms. Conclusions: In addition to significantly improving PFS and ORR, overall QoL was maintained in pts treated with ALP + FUL. Clinical trial information: NCT02437318.