On September 25, 2026 C4 Therapeutics, Inc. (C4T) (Nasdaq: CCCC), a clinical-stage biopharmaceutical company dedicated to advancing targeted protein degradation (TPD) science, reported new biomarker data today from its Phase 1 clinical trial of cemsidomide in combination with dexamethasone in patients with relapsed/refractory multiple myeloma (RRMM) in a poster presentation at the 23rd IMS Annual Meeting. In addition, the poster included preliminary biomarker data from the first two patients in the ongoing Phase 1b trial of cemsidomide in combination with elranatamab (ELREXFIO). These data further build upon the body of evidence supporting cemsidomide’s immunomodulatory activity and potential as a combination partner.

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"Immune-based therapies have transformed the treatment landscape for multiple myeloma, however T-cell exhaustion is associated with both primary resistance and relapse in these patients. Maintaining T-cell fitness is an important component of achieving deep and durable responses," said Len Reyno, M.D., chief medical officer of C4 Therapeutics. "The totality of data presented today demonstrate that cemsidomide activates immune cell function, consistent with the hypothesis that cemsidomide will enhance the clinical benefit of immune-based therapies when used in combination. Additionally, clearing the 75 µg cemsidomide dose level in our Phase 1b trial is a critical step forward in identifying an effective and safe dose of cemsidomide in combination with a BCMA-directed T-cell engager, like elranatamab. Collectively, these outcomes, along with the differentiated safety profile and compelling anti-myeloma activity observed in our Phase 1 trial, reinforce our development strategy to potentially establish cemsidomide as a backbone therapy in multiple myeloma for patients in need of new treatment options."

IMS Data Highlights and Cemsidomide Trial Progress Update:

Phase 1 Trial of Cemsidomide in Combination with Dexamethasone
In 62 heavily pre-treated RRMM patients across the once-daily (QD) dose levels, cemsidomide demonstrated coordinated activation of T cells, including CD8+ T cells, and functional reprogramming of natural killer (NK) cells. Notably, enhanced immune cell function was observed at the highest dose levels studied (75 µg and 100 µg), which also achieved compelling overall response rates in the Phase 1 trial.

Phase 1b Trial of Cemsidomide in Combination with Elranatamab
Biomarker data from the first two patients showed that cemsidomide drives the expansion and activation of CD8+ effector memory T cells as measured by elevated HLA-DR and prevents T-cell exhaustion as measured by PD-1, TIM-3 and LAG3 expression.(1) These initial findings provide positive translational and mechanistic support for cemsidomide as a potential combination partner for immune-based therapies.

In addition, following the completion of the first safety cohort evaluating six patients, the safety data review committee declared the 75 µg cemsidomide dose level in combination with elranatamab safe. The Phase 1b trial is now advancing into a dose escalation safety cohort at the 100 µg cemsidomide dose level and an expansion cohort at the 75 µg cemsidomide dose level. Data from all cohorts evaluated in the Phase 1b trial are expected in mid-2027.

About Cemsidomide
Cemsidomide is an investigational oral cereblon-modulating protein degrader of IKZF1/3, transcription factors foundational to multiple myeloma biology. Data from the fully enrolled Phase 1 trial show cemsidomide’s differentiated safety and tolerability profile and potentially class-leading anti-myeloma activity that supports the potential for durable outcomes.

About Cemsidomide in Combination with Elranatamab (ELREXFIO)
The Phase 1b trial is designed to evaluate the safety, tolerability and preliminary efficacy of cemsidomide and dexamethasone in combination with elranatamab, an FDA-approved B-cell maturation antigen CD3 targeted bispecific antibody. Data generated from the cemsidomide Phase 1 trial in relapsed/refractory multiple myeloma demonstrate robust T-cell activation and cytokine expression across multiple doses. By activating immune T-cells, cemsidomide, when combined with a BCMAxCD3 bispecific such as elranatamab, may amplify the anti-myeloma immune response and lead to deeper and more durable responses. The study will evaluate different cemsidomide dose levels (beginning with 75 µg, with the opportunity to simultaneously explore 50 µg and 100 µg) in patients who have received one to four prior lines of therapy, which must have consisted of at least one IKZF1/3 degrader. Exclusion criteria for patients include those who have received prior treatment with a BCMA-directed T-cell engager or BCMA-directed CAR-T therapy. More information is available at clinicaltrials.gov (NCT07280013).

About Multiple Myeloma
Multiple myeloma is a blood cancer that affects plasma cells in the bone marrow. It is the second most common blood cancer, with approximately 36,000 people in the United States diagnosed each year. Multiple myeloma is characterized by cycles of remission and relapse, which leads to patients needing multiple lines of therapy to manage the persistent disease. More than 175,000 patients in the United States are estimated to be living with or in remission from myeloma. However, despite treatment advances, approximately 40% of patients do not survive beyond five years.

(Press release, C4 Therapeutics, SEP 25, 2026, View Source [SID1234671083])