C4 Therapeutics (CCCC) said Phase 1 data to be presented at the European Hematology Association 2026 Congress showed its investigational drug cemsidomide achieved a 53% overall response rate at the recommended Phase 2 dose in heavily pretreated patients with relapsed or refractory multiple myeloma, the company said Thursday.

The study included 73 heavily pretreated patients with a median of seven prior therapies, with 75% previously treated with BCMA-directed therapy and 75% previously treated with CAR-T or T-cell engager therapies, showing a 36% overall response rate across all doses, with deeper responses at higher dose levels, the company said.

C4 Therapeutics said cemsidomide showed a manageable safety profile, with no discontinuations deemed related to cemsidomide and minimal dose reductions related to safety or tolerability, and noted complete responses and MRD negativity at the 100 microgram dose level.

The data support continued development of cemsidomide in relapsed or refractory multiple myeloma, with further studies across lines of therapy and in combination with approved therapies planned, it added.