Antitumor activity and safety of sirolimus for solid tumors with PIK3CA mutations: A multicenter, open-label, prospective single-arm study (KM 02-01, KCSG UN17-16)

Background: PIK3CA contributes to cell growth via the PI3K-AKT-mammalian target of rapamycin (mTOR) signaling pathway. Mutations in the pathway are frequently observed in solid tumors. We assessed the efficacy and safety of sirolimus, an mTOR inhibitor, in chemotherapy-refractory solid tumors with PIK3CA mutations or amplifications. Methods: This was an open-label, single-arm, multicenter pilot study. Twenty-four patients with solid tumors harboring a PIK3CA mutation were treated with sirolimus between July 2017 and March 2019. Treatment was continued until disease progression, unacceptable adverse events, or death. The primary end points were the overall response rate (ORR), disease control rate (DCR), and safety. Results: The median follow-up time was 6.1 months. Two patients with rapid disease progression-related death, one who withdrew, and one with a non-target lesion only were excluded from the analysis. Among 20 evaluable patients, 6 patients showed stable disease and 14 showed progressive disease (ORR 0%, DCR 30%). The median progression-free survival was 2.39 months (95% confidence interval, 1.97-2.81 months). The most common adverse event was abdominal pain (20.8%), followed by anemia (16.7%) and fatigue (16.7%). The adverse events were generally manageable. Conclusions: Although safe, sirolimus monotherapy did not show meaningful antitumor activity in chemotherapy-refractory solid tumors with PIK3CA mutations. Combinations of mTOR inhibitors for stabilization and other antitumor agents with beneficial effects on tumor volume may improve outcomes.