1040 Background: In the phase 3 SOLAR-1 study, ALP + fulvestrant (FUL) improved PFS in pts with HR+, HER2– ABC with a PIK3CA mutation overall and in the small group of pts with prior cyclin-dependent kinase 4/6 inhibitor (CDKi) use. We report interim data from the BYLieve study in pts with PIK3CA-mutated ABC and prior CDKi exposure. Methods: BYLieve is an ongoing, phase 2, open-label, non-comparative study of ALP 300 mg QD + ET in men and women with PIK3CA-mutated HR+, HER2– ABC whose disease progressed on/after CDKi + ET. Pts are permitted ≤2 prior anticancer therapies and ≤1 prior chemotherapy regimen for ABC. Pts with prior CDKi and AI ( FUL cohort) receive ALP and FUL 500 mg Q28d + C1d15 IM. Pts with prior CDKi and FUL ( LET cohort) receive ALP and letrozole (LET) 2.5 mg PO QD. In this preplanned interim analysis, conducted after ≥20 pts in FUL had ≥6 mo of follow-up, descriptive data are reported for preliminary safety and efficacy in the FUL and LET cohorts. Results: At data cutoff, 64 and 36 pts were enrolled in the FUL and LET cohorts, respectively; 39 pts ( FUL, n = 21; LET, n = 18) have safety and efficacy data with ≥6 mo follow-up and are reported here. Data on 100 pts enrolled at the time of data cutoff will be presented. In the 39 pts with ≥6 mo follow-up, median ALP duration was 5.3 and 5.5 mo in FUL and LET, respectively; median duration of FUL and LET was 5.6 mo. Median relative ALP dose intensity was 93% ( FUL) and 87% ( LET). Most common grade ≥3 adverse events were hyperglycemia (38.1% ( FUL) and 27.8% ( LET)) and rash (4.8% ( FUL) and 27.8% ( LET)). Only 2 pts (5%; 1 pt per cohort) discontinued due to an AE. In pts with centrally confirmed PIK3CA mutation (n = 20 ( FUL); n = 17 ( LET)), ORR was 20% ( FUL) and 18% ( LET), CBR was 40% ( FUL) and 35% ( LET). Efficacy and safety data for the 100 enrolled pts will be presented at the meeting. Conclusions: Pending further readout of the ongoing BYLieve trial, safety and tolerability of ALP and hormonal therapy in pts with prior CDKi are consistent with those of SOLAR-1; discontinuation due to toxicity was rare. NCT03056755. Clinical trial information: NCT02437318.

Conclusions:In pts receiving first-line ET across the ML trials, RIB delayed deterioration in QOL. TTDD for GHS, pain, and emotional functioning scores was longer with RIB vs. PBO. Overall, this large, robust analysis demonstrated favorable QOL results with the addition of RIB to ET in patients with HR+/HER2À ABC.

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Association of quality of life (QOL) with overall survival (OS) in patients (pts) with HR+/HER2L advanced breast cancer (ABC) treated with ribociclib (RIB) + endocrine therapy (ET) in the MONALEESA-3 (ML-3) and ML-7 trials