C4 Therapeutics, Inc. (C4T) (NASDAQ:CCCC), a clinical-stage biopharmaceutical company dedicated to advancing targeted protein degradation science, today announced that the first patient has been dosed with cemsidomide, an oral IKZF1/3 degrader, in a Phase 1b trial evaluating cemsidomide and dexamethasone in combination with elranatamab (ELREXFIO®), an FDA-approved B-cell maturation antigen CD3 targeted bispecific antibody, for the treatment of relapsed/refractory multiple myeloma (RRMM).

"Data from our Phase 1 trial support cemsidomide as a potential best-in-class, next-generation IKZF1/3 degrader and the initiation of this Phase 1b trial, along with our late-line Phase 2 MOMENTUM trial, enable an efficient path toward bringing cemsidomide to growing myeloma patient populations across multiple lines of therapy," said Len Reyno, M.D., chief medical officer of C4 Therapeutics. "Bispecific T-cell engagers have quickly become a critical treatment pillar in multiple myeloma while IKZF1/3 degraders remain foundational therapies across multiple lines and combination regimens in multiple myeloma. In this combination with elranatamab, we see an opportunity to leverage cemsidomide's potent direct anti-myeloma effect and its ability to enhance the immune environment which has the potential to deliver a deeper and more durable therapeutic response for patients, including those in earlier lines of therapy."

The Phase 1b trial is an open-label, multicenter study to establish an optimal dose for cemsidomide in combination with elranatamab by evaluating the safety and tolerability as well as preliminary anti-myeloma activity of cemsidomide in combination with elranatamab in RRMM patients. The trial will enroll up to 54 patients to evaluate cemsidomide in combination with elranatamab, beginning at the 75 µg dose of cemsidomide with the opportunity to explore 50 µg and 100 µg doses of cemsidomide. The primary endpoint is to assess the safety and tolerability of cemsidomide in combination with elranatamab. Secondary endpoints will evaluate anti-myeloma activity per the International Myeloma Working Group (IMWG) response criteria, which will include the overall response rate, minimal-residual disease (MRD)-negative complete response rate, duration of response and other relevant measures. In October 2025, C4T and Pfizer entered into a clinical trial collaboration supply agreement under which Pfizer provides elranatamab at no cost while C4T sponsors and conducts the clinical trial. Phase 1b data from all cohorts evaluating cemsidomide in combination with elranatamab is anticipated in mid-2027.

The Phase 1b trial is part of a broader developmental strategy to support cemsidomide's use across multiple lines of treatment. This strategy also includes the ongoing Phase 2 MOMENTUM Trial investigating the use of cemsidomide and dexamethasone in the fourth line of treatment or later. In addition to these two trials, C4T intends to evaluate cemsidomide in combination with other anti-myeloma agents, and remains on track to share these plans in mid-2026.