Key Highlights

● Biomarker Data:: C4 Therapeutics presented new data showing cemsidomide activated T cells and reprogrammed natural killer cells in relapsed or refractory multiple myeloma patients.

● Phase 1 Results:: In 62 heavily pre-treated patients, the highest dose levels of 75 and 100 micrograms showed coordinated T-cell activation and NK-cell reprogramming.

● Phase 1b Signal:: Early data from the first two patients in the elranatamab combination study, as of June 22, 2026, showed CD8-positive T-cell expansion without rising exhaustion markers.

● Safety Clearance:: The trial's safety review committee cleared the 75-microgram combination dose, allowing further dose-escalation and expansion cohorts, with complete Phase 1b data expected mid-2027.

C4 Therapeutics, Inc. (NASDAQ:CCCC) disclosed in an 8-K filed September 25, 2026 that it presented new biomarker data from two Clinical Trials of its drug cemsidomide, alone with dexamethasone and in combination with elranatamab, at the 23rd International Myeloma Society Annual Meeting, showing activation of T cells and reprogramming of natural killer cells in patients with relapsed or refractory multiple myeloma.

What the Phase 1 Data Showed

In the Phase 1 trial, cemsidomide was studied in 62 heavily pre-treated patients with relapsed/refractory multiple myeloma. At the highest dose levels tested, 75 and 100 micrograms, the data showed what the company describes as coordinated activation of T cells, including CD8-positive T cells, along with functional reprogramming of natural killer cells, immune mechanisms the company says are consistent with enhanced anti-tumor immune activity.

Early Signals From the Phase 1b Combination Study

The Phase 1b trial is testing cemsidomide in combination with elranatamab, another myeloma therapy, at dose levels of 50, 75 and 100 micrograms in patients who have received one to four prior lines of therapy. Early biomarker data from the first two patients, collected as of June 22, 2026, showed that cemsidomide drives expansion and activation of CD8-positive effector memory T cells while preventing the T-cell exhaustion markers PD-1, TIM-3 and LAG3 from rising, a sign, according to the company, that the immune cells retain their function rather than becoming worn down.

Safety Clearance and Next Steps

Following a review, the trial's safety review committee cleared the 75-microgram dose of cemsidomide in combination with elranatamab, allowing the Phase 1b study to advance into further dose-escalation and expansion cohorts. The company says complete data from all Phase 1b cohorts is expected in mid-2027.

What the Company Said, and the Disease Context

Chief Medical Officer Len Reyno said, "Maintaining T-cell fitness is an important component of achieving deep and durable responses," and that cemsidomide "activates immune cell function, consistent with hypothesis that it will enhance clinical benefit of immune therapies." The company cites a large unmet need in multiple myeloma, noting that about 36,000 people are diagnosed with the disease annually in the United States, more than 175,000 are living with or in remission from it, and roughly 40% of patients do not survive beyond five years of diagnosis.

What Isn't Yet Known

The data presented are early and drawn from small subsets of patients, particularly the two-patient snapshot from the Phase 1b combination cohort; the filing does not report objective response rates, progression-free survival, or other efficacy endpoints tied to this biomarker data. C4 Therapeutics is a Watertown, Massachusetts-based, Delaware-incorporated biopharmaceutical company.

Why Biomarker Data Matters at This Stage

Cemsidomide belongs to a class of drugs designed to modulate the immune system rather than directly kill tumor cells, so biomarker measurements of T-cell and NK-cell activity serve as early mechanistic evidence that the drug is doing what it was designed to do, ahead of larger studies that would establish clinical efficacy endpoints like response rates or survival. Presenting this data at a major medical meeting like the International Myeloma Society Annual Meeting is a common way for a clinical-stage biopharmaceutical company to build a scientific case for a drug candidate's mechanism while larger efficacy datasets are still being collected.

Awaiting Complete Phase 1b Data in Mid-2027

The key milestone ahead is mid-2027, when the company expects complete data from all Phase 1b dosing and expansion cohorts. Investors should also watch for enrollment progress in the dose-escalation cohorts now open following the safety committee's clearance of the 75-microgram combination dose.