Avapritinib versus midostaurin or cladribine in advanced systemic mastocytosis: A retrospective real-world external control study.

As there are no prospective randomized studies in patients with advanced systemic mastocytosis (AdvSM), we compared clinical outcomes between patients treated with avapritinib in the Phase I EXPLORER (NCT02561988) and Phase II PATHFINDER (NCT03580655) trials (N = 176) and patients treated with midostaurin (N = 99) or cladribine (N = 49) from a global, multi-center, retrospective, chart review study. Overall survival (OS) and duration of treatment (DOT) were compared between the cohorts using inverse probability of treatment weighting (IPTW)-adjusted Cox proportional hazards models, and maximum reduction in serum tryptase levels was compared using adjusted generalized linear models. Median OS was not reached (95% confidence interval [CI]: 46.9 months, not estimable) for avapritinib, 28.6 (18.2, 44.6) months for midostaurin, and 23.4 (14.8, 40.6) months for cladribine. The avapritinib cohort had significantly longer OS compared to midostaurin (hazard ratio [HR] [95% CI]: 0.59 [0.36, 0.97]) and cladribine (0.32 [0.15, 0.67]), longer DOT (vs. midostaurin: 0.63 [0.41, 0.96]; vs. cladribine: 0.14 [0.09, 0.23]), and greater reduction in serum tryptase levels with mean difference [95% CI] vs. midostaurin of -72.8 % [-101.1 %, -44.6 %] and vs. cladribine of -25.0 % [-32.4 %, -17.7 %] (all p < 0.05). Results were similar in treatment-naïve (1 L) and previously treated (2 L+) patients; there was improved OS in 1 L avapritinib vs. 1 L midostaurin patients (HR: 0.14 [0.05, 0.42]; p < 0.001) and in 2 L+ avapritinib vs. 2 L+ cladribine patients (0.34 [0.16, 0.71]; p = 0.004). Together, we show that avapritinib treatment resulted in significantly improved OS, longer DOT, and greater reduction in serum tryptase levels compared to midostaurin or cladribine in real-world clinical practice.