Abstract PO2-19-09: INAVO122: a Phase III study of maintenance inavolisib or placebo + pertuzumab + trastuzumab following induction with pertuzumab + trastuzumab + a taxane in patients with PIK3CA-mutated, HER2-positive advanced breast cancer

Abstract Background The PI3K pathway plays a crucial role in HER2 signaling. Somatic mutations of PIK3CA, the gene that encodes the PI3K p110α subunit, may induce resistance to HER2-targeted therapies and are associated with poorer clinical outcomes (Swain SM, et al. SABCS 2022; P2-11-07). Inavolisib, a potent p110α-selective inhibitor that induces degradation of mutant p110α, has shown antitumor activity in PIK3CA-mutated HER2-positive breast cancer (HER2+ BC) and long-term tolerability with early intervention for common on-class toxicities, including hyperglycemia, diarrhea, and stomatitis (Bedard P, et al. ASCO 2022; 1052). The current study will assess the efficacy and safety of maintenance inavolisib + fixed-dose combination of pertuzumab + trastuzumab for subcutaneous injection (PH FDC SC) after first-line induction treatment in patients with PIK3CA-mutated, HER2+, advanced BC (aBC). Trial design INAVO122 is a multicenter, randomized, international, double-blind, placebo-controlled study. Patients will be enrolled for: first-line induction treatment if they are receiving/will receive PH + a taxane; or maintenance treatment completing induction treatment. In the maintenance phase, patients will be randomized 1:1 to receive inavolisib (9 mg orally once daily; Days 1–21 of 21-day cycles) + PH FDC SC (every 3 weeks), or placebo + PH FDC SC. Study treatment will continue until disease progression, unacceptable toxicity, death, consent withdrawal, or at the investigator’s discretion. ELIGIBILITY Enrolled patients must have centrally determined HER2+, PIK3CA-mutated tumors, with documented hormone receptor status per local assessment, and be disease-free for ≥ 6 months from completion of neoadjuvant/adjuvant systemic non-hormonal treatment. They must not have received any treatment for aBC prior to induction, and, at screening, fasting glucose must be 126 mg/dL and HbA1c 6.4%. To be randomized, patients must have completed induction therapy per standard of care without progression of disease and show left ventricular ejection fraction ≥ 50%. AIMS The primary endpoint is investigator-assessed progression-free survival. Secondary endpoints are overall survival; investigator-assessed objective response rate, duration of response, clinical benefit rate, and time to second disease progression; health-related quality of life; safety; and pharmacokinetics. STATISTICAL METHODS The primary endpoint analysis will utilize a two-sided stratified log-rank test at a two-sided significance level of 5%. A stratified Cox proportional hazards model will be used to estimate the hazard ratio between the two treatment arms and its 95% confidence intervals. ACCRUAL Target randomization is ~230 patients; recruitment began in July 2023. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT05894239. Citation Format: Sandra Swain, Carlos Barrios, Reva Basho, Giuseppe Curigliano, Nadia Harbeck, Chiun-Shen Huang, Sherene Loi, Nicholas Turner, Jessica Chen, Volkmar Henschel, Simon Warburton, Fabiola Amair-Pinedo, Javier Cortés. INAVO122: a Phase III study of maintenance inavolisib or placebo + pertuzumab + trastuzumab following induction with pertuzumab + trastuzumab + a taxane in patients with PIK3CA-mutated, HER2-positive advanced breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-19-09.