C4 Therapeutics to Present New Biomarker Data on the Immunomodulatory Effects of Cemsidomide in Combination with Dexamethasone from its Phase 1 Relapsed/Refractory Multiple Myeloma Trial at the 23rd International Myeloma Society (IMS) Annual Meeting

C4 Therapeutics, Inc. (C4T) (Nasdaq: CCCC), a clinical-stage biopharmaceutical company dedicated to advancing targeted protein degradation (TPD) science, today announced that new biomarker data on the immunomodulatory effects of cemsidomide in combination with dexamethasone from its Phase 1 trial for relapsed/refractory multiple myeloma (RRMM) will be presented in a poster at the 23 rd IMS Annual Meeting. The data characterize the immune effects on T cells and natural killer (NK) cells across the once-daily dose levels evaluated in the Phase 1 trial, further supporting cemsidomide’s potential as a combination partner for immune-based therapies. The meeting will take place in Glasgow, Scotland from September 23 – 26, 2026.

Poster Presentation Details: Title : T- And NK-Cell Immunomodulatory Reprogramming By Cemsidomide, A Novel And Potent MonoDAC ® Degrader, In Relapsed/Refractory Multiple Myeloma: Biomarker Results From CFT7455-1101 Arm B2 Cohort. Presentation Date and Time : September 25, 2026, from 12 pm – 1 pm BST / 7 am – 8 am ET Presenter : Riadh Lobbardi, Ph.D., Senior Director of Translational Medicine, C4 Therapeutics

About Cemsidomide Cemsidomide is an investigational, next-generation orally bioavailable MonoDAC ® degrader (molecular glue) 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 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.

About C4 Therapeutics C4 Therapeutics (C4T) (Nasdaq: CCCC) is a clinical-stage biopharmaceutical company dedicated to delivering on the promise of targeted protein degradation science to create a new generation of medicines that transforms patients’ lives. C4T is progressing targeted oncology programs through clinical studies and leveraging its TORPEDO ® platform to efficiently design and optimize small-molecule medicines to address difficult-to-treat diseases. C4T’s degrader medicines are designed to harness the body’s natural protein recycling system to rapidly degrade disease-causing proteins, offering the potential to overcome drug resistance, drug undruggable targets and improve patient outcomes. For more information, please visit www.c4therapeutics.com.

Contacts: Investors: Courtney Solberg Associate Director, Investor Relations [email protected]

Media: Loraine Spreen Senior Director, Corporate Communications & Patient Advocacy [email protected]