1003 Background: INAVO120 (NCT04191499) showed significantly and meaningfully improved investigator-assessed progression-free survival (PFS; stratified hazard ratio 0.43) with Inavo+Palbo+Fulv v Pbo+Palbo+Fulv, and manageable safety and tolerability. To further characterize the substantial benefit/risk of the Inavo triplet, we assessed additional clinically relevant efficacy endpoints, detailed safety data of key adverse events (AEs) for Inavo (hyperglycemia [HG], diarrhea, rash, stomatitis), and pt-reported outcomes (PROs). Methods: Efficacy endpoints includedtime from randomization to end of next-line treatment (tx; proxy for PFS2) and to first chemotherapy (TTFC). Key AEs were reported by grouped terms. PROs were assessed by PRO-CTCAE, an overall bother item, BPI-SF, and EORTC QLQ-C30. Results: Increases in median “PFS2” (24.0 v 15.1 mo; unstratified hazard ratio: 0.59 [95% CI, 0.42–0.83]) and TTFC (NE v 15.0 mo; unstratified hazard ratio: 0.53 [95% CI, 0.37–0.78]) were observed in the Inavo v Pbo arm (median follow-up: 21.3 mo; Table). Key AEs were mostly G1–2 and had resolved (Table). No key AEs were G4–5. In the Inavo arm, among pts who experienced key AEs (HG, diarrhea, rash, stomatitis), median time to first onset was 7, 15, 29, and 13 days, respectively. The key AEs were managed with standard supportive care and Inavo dose interruptions/reductions. One pt discontinued Inavo due to HG; one, due to stomatitis. Pts receiving Inavo experienced a longer duration of time without worsening pain severity and maintained their day-to-day functioning and health-related quality of life on tx. Most pts in both arms reported levels of selected symptomatic AEs from the PRO-CTCAE and overall tx bother as moderate or less, indicating that Inavo does not contribute additional tx burden. Conclusions: Inavo+Palbo+Fulv was associated with sustained benefit beyond disease progression, delaying chemotherapy administration, with manageable safety and tolerability that was reflected in PROs; hence, supporting it as a new standard of care. Clinical trial information: NCT04191499 . [Table: see text]

First-line inavolisib/placebo + palbociclib + fulvestrant (Inavo/Pbo+Palbo+Fulv) in patients (pts) with <i>PIK3CA</i>-mutated, hormone receptor-positive, HER2-negative locally advanced/metastatic breast cancer who relapsed during/within 12 months (mo) of adjuvant endocrine therapy completion: INAVO120 Phase III randomized trial additional analyses.