C4 Therapeutics Announces Biomarker Data from Cemsidomide MM Trials

What Happened

• On September 25, 2026, C4 Therapeutics (CCCC) announced and posted a press release and corporate presentation reporting new biomarker data from its Phase 1 trial of cemsidomide plus dexamethasone and preliminary biomarker and safety data from the Phase 1b trial of cemsidomide plus elranatamab (ELREXFIO®), presented at the 23rd International Myeloma Society Annual Meeting.
• The Phase 1 data (62 heavily pre-treated RRMM patients across once-daily dose levels) showed coordinated activation of T cells (including CD8+ T cells) and functional reprogramming of NK cells, with enhanced immune function observed at the highest dose levels (75 µg and 100 µg) that also produced “compelling” overall response rates. The Phase 1b biomarker readout (data cutoff June 22, 2026) from the first two patients showed expansion/activation of CD8+ effector memory T cells (elevated HLA-DR) and reduced markers of T‑cell exhaustion (PD‑1, TIM‑3, LAG3). After a six‑patient safety cohort, the 75 µg dose with elranatamab was declared safe and the trial is advancing into a 100 µg dose‑escalation cohort and a 75 µg expansion cohort; full Phase 1b cohort data are expected mid‑2027.

Key Details

• Filing date: September 25, 2026 (8-K disclosing press release and presentation).
• Phase 1 (cemsidomide + dexamethasone): 62 heavily pre-treated RRMM patients; immune activation strongest at 75 µg and 100 µg dose levels.
• Phase 1b (cemsidomide + elranatamab): biomarker data from first 2 patients (data as of June 22, 2026); 75 µg dose declared safe after initial 6‑patient safety cohort; trial now moving to 100 µg escalation and 75 µg expansion.
• Timing: Data from all Phase 1b cohorts expected in mid‑2027.

Why It Matters

• For investors, these results provide early biological evidence that cemsidomide can boost immune cell activity and may be a viable partner with immune therapies like elranatamab. Safety clearance at the 75 µg dose and planned dose escalation are important operational milestones that keep the program on track for additional data in mid‑2027. The company also highlighted the usual forward‑looking statement risks in the filing, reminding investors that early biomarker or activity signals may not predict long‑term clinical benefit.