Ipatasertib combined with non-taxane chemotherapy for patients with previously treated advanced triple-negative breast cancer: the PATHFINDER phase IIa trial

The PI3K/AKT pathway is frequently altered in advanced triple-negative breast cancer (aTNBC), representing a promising target. Ipatasertib, a pan-AKT inhibitor, has shown activity with taxane-based chemotherapy and acceptable safety. This study evaluated the safety and efficacy of ipatasertib with non-taxane chemotherapy for aTNBC. The PATHFINDER trial was a multicenter, open-label, non-comparative, phase IIa study with a safety run-in phase. Eligible patients had TNBC pretreated in the advanced setting with one or two chemotherapy regimens, including a taxane, and no prior exposure to PI3K/mTOR/AKT inhibitors. Patients received 21-day cycles of ipatasertib combined with capecitabine (arm A), eribulin (arm B), or carboplatin plus gemcitabine (arm C). The safety run-in phase determined feasibility and phase IIa doses. The primary endpoint was the incidence of treatment-emergent adverse events (TEAEs). Key secondary endpoints included progression-free survival (PFS), overall survival (OS), and objective response rate (ORR). The analysis was exploratory without formal hypothesis testing. A total of 54 patients were assigned to arms A (N = 22), B (N = 25), and C (N = 7). Arm C was discontinued due to toxicity during the safety run-in phase. At data cut-off (November 2023), the overall median follow-up was 12.1 (range: 0.2-35.6) months. Common TEAEs in arm A were diarrhea (59.1%, 0.0% G ≥ 3), fatigue (36.4%, 0.0% G ≥ 3), and nausea (36.4%, 0.0% G ≥ 3); in arm B neutropenia (52.0%; 32.0% G ≥ 3), diarrhea (52.0%, 4.0% G3) and stomatitis (44.0%; 8.0% G3); and in arm C thrombocytopenia (85.7%, 85.7%G ≥ 3), anemia (85.7%, 57.1% G ≥ 3), neutropenia (71.4%, 71.4% G ≥ 3). No treatment-related deaths occurred. Median PFS was 2.7 (95%CI, 1.5-4.1) and 3.8 (95%CI, 1.5-9.6) months; median OS was 15.5 (95%CI, 11.8-19.3) and 11.5 (95%CI, 8.8-25.1) months; and ORR was 9.1% and 36.0% for arms A and B, respectively. No significant differences in efficacy were observed by PIK3CA mutational status. Ipatasertib combined with capecitabine or eribulin showed acceptable safety but was not tolerable with carboplatin plus gemcitabine. The addition of ipatasertib to capecitabine or eribulin shows a potential efficacy signal in this patient population, compared to historical monotherapy data of these treatments. Identifying biomarkers to predict response to AKT inhibitors in TNBC is crucial. www. gov , NCT04464174. Registered 09 July 2020.