A randomised phase II trial of selumetinib vs selumetinib plus temsirolimus for soft-tissue sarcomas

Background: The MEK inhibitor, selumetinib, suppresses soft-tissue sarcoma (STS) cell proliferation in vitro. Mammalian target of rapamycin inhibitors possess modest activity against STS; however, resistance develops via MAPK pathway feedback activation. The combination of selumetinib and temsirolimus synergistically inhibits STS cell line growth. Therefore, a randomized phase II trial of selumetinib vs selumetinib plus temsirolimus was conducted. Methods: Seventy-one adults with advanced STS who received <= 2 prior chemotherapeutics were randomized to selumetinib 75 mg p.o. bid and allowed to crossover upon progression, or to selumetinib 50 mg p.o. bid plus temsirolimus 20 mg i.v. weekly, with primary endpoint of progression-free survival (PFS). Results: There was no difference in PFS between the two arms for the overall cohort (median 1.9 vs 2.1 months); an improved median PFS was observed in the combination arm (N - 11) over single agent (N - 10) in the prespecified leiomyosarcoma stratum (median 3.7 vs 1.8 months; P = 0.01). Four-month PFS rate was 50% (95% confidence interval 0.19-0.81) with the combination vs 0% with selumetinib alone in the leiomyosarcoma cohort. Most common grade 3/4 adverse events with the combination were mucositis (29%), lymphopenia (26%), neutropenia and anaemia (20% each). Conclusions: While single-agent selumetinib has no significant activity in STS, the combination may be active for leiomyosarcomas.