C4 Therapeutics has begun dosing in a Phase Ib study assessing cemsidomide and elranatamab (Elrexfio) in patients with relapsed or refractory multiple myeloma (r/r MM).
The multi-centre, open-label trial aims to determine an optimal dose for cemsidomide when used alongside elranatamab by assessing preliminary anti-myeloma activity, tolerability, and safety.
It will enrol around 54 patients to study cemsidomide, an oral ikaros family zinc finger protein 1/3 (IKZF1/3) degrader, along with elranatamab, a B-cell maturation antigen cluster of differentiation 3 (CD3) -targeted bispecific antibody, both with dexamethasone.
Dose levels under evaluation include 50µg, 75µg and 100µg of cemsidomide. The primary endpoint focuses on the combination's safety and tolerability.
Secondary endpoints will measure anti-myeloma activity according to response criteria set by the International Myeloma Working Group. This includes overall response rate, minimal-residual disease-negative complete response rate and duration of response.
C4 Therapeutics expects to report Phase Ib data from all cohorts by mid-2027.
Under an agreement signed in October 2025, Pfizer supplies elranatamab at no cost while C4 Therapeutics sponsors and manages the study.
The study forms part of a broader strategy to evaluate cemsidomide across several lines of treatment, which includes the ongoing Phase II MOMENTUM trial investigating cemsidomide with dexamethasone in fourth-line or later therapies.
C4 Therapeutics also plans to assess cemsidomide in combination with additional anti-myeloma agents, targeting more comprehensive data and strategy updates by mid-2026.
C4 Therapeutics' chief medical officer Len Reyno said: “Data from our Phase I trial support cemsidomide as a potential best-in-class, next-generation IKZF1/3 degrader and the initiation of this Phase Ib trial, along with our late-line Phase II MOMENTUM trial, enables an efficient path toward bringing cemsidomide to growing myeloma patient populations across multiple lines of therapy.
“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.”
Last month, C4 Therapeutics dosed the first patient in its Phase II MOMENTUM trial of cemsidomide, combined with dexamethasone for patients with r/r MM.
