STC-15 is the world’s first RNA-modifying enzyme inhibitor to reach human trials. Phase 1 showed durable tumour regression across multiple sarcoma subtypes. The $56M Series C is backed entirely by existing investors including Pfizer Ventures and M Ventures.

STORM Therapeutics, a Cambridge-based clinical-stage biotech targeting RNA modifications to treat cancer, has raised $56 million in a Series C round and dosed the first patient in a Phase 2 clinical trial of its lead drug, STC-15, in selected sarcoma indications.

The round was funded entirely by existing investors: M Ventures, Pfizer Ventures, Taiho Ventures LLC, IP Group plc, the UTokyo Innovation Platform Co., Ltd. (UTokyo IPC), and Fast Track Initiative (FTI).

STC-15 is a first-in-class, oral small-molecule inhibitor of METTL3 – an enzyme that methylates messenger RNA and plays a central role in cancer stem cell differentiation. It is the first RNA-modifying enzyme inhibitor ever to enter human clinical trials, having commenced its Phase 1 study in November 2022.

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METTL3 adds a chemical tag called m6A to mRNA, influencing how cells read genetic instructions; in certain cancers, this process is hijacked to keep malignant progenitor cells locked in a proliferative, undifferentiated state. Inhibiting METTL3 disrupts this process, pushing cancer cells towards cycle arrest and programmed death.

Sarcomas, cancers arising from bone or soft tissue including muscle, fat, cartilage, and blood vessels, account for 1% of adult cancers and 15% of paediatric cancers.

They are notoriously difficult to treat because they frequently lack the driver mutations or immunogenic features that make most solid tumours amenable to targeted therapy or immunotherapy.

STORM’s thesis is that sarcomas are particularly dependent on METTL3-driven mRNA methylation for their growth and survival, making them a biologically compelling target for STC-15. In Phase 1, the drug demonstrated durable tumour regression across multiple sarcoma subtypes across dose levels between 60mg and 200mg taken three times weekly.

Full Phase 1 results are expected to be presented at a medical conference in 2026.

The Phase 2 monotherapy trial is designed to support a potential accelerated regulatory approval pathway for STC-15, and to build a foundation for expanding clinical development into additional oncology indications. The first patient has now been successfully dosed. The trial’s ClinicalTrials.gov identifier is NCT06975293.

STC-15 is simultaneously being evaluated in a Phase 1b/2 combination study with LOQTORZI (toripalimab), a PD-1 inhibitor from Coherus BioSciences, across non-small cell lung cancer, head and neck squamous cell carcinoma, melanoma, and endometrial cancer, a collaboration announced in May 2025. 

Jonathan Trent, MD of the University of Miami’s Sylvester Comprehensive Cancer Center and a clinical investigator on the trial, said STC-15’s mechanism “targets sarcomas at their vulnerability, reprogramming malignant cells toward cell cycle arrest and apoptosis.”

STORM CEO Jerry McMahon described the Phase 2 dosing as “a pivotal breakthrough in tackling cancers characterised by aberrant cell differentiation,” pointing to the unmet need in sarcoma where existing options remain limited.