STC-15

Subset analysis shows early clinical activity supported by biomarker evidence of targeting cancer stem cell pathways driving tumor growth and progression CAMBRIDGE, United Kingdom, May 22, 2026 (GLOBE NEWSWIRE) -- STORM Therapeutics Ltd. (STORM), the clinical stage company targeting RNA modifications to reprogram cells and develop novel cancer therapies, today announces that a subset analysis of sarcoma patients enrolled in the Phase 1 dose escalation study of its lead candidate, STC-15, will be presented at the American Society of Clinical Oncology (ASCO) Annual Meeting , taking place May 29 – June 2, 2026 in Chicago, Illinois. The presentation, titled ‘A Subset Analysis of Clinical Activity and Pharmacodynamic Biomarkers in Patients with Sarcomas in the Phase 1 Dose Escalation Study of STC-15, a METTL3 Inhibitor’ , will report clinical activity alongside pharmacodynamic (PD) and epitranscriptomic findings from sarcoma patients treated with STC-15, a first-in-class, oral small-molecule inhibitor of the RNA methyltransferase METTL3. The Phase 1 study enrolled 42 patients with advanced malignancies across five dose‑escalation cohorts ranging from 60 mg to 200 mg and evaluated both daily and three‑times‑weekly oral dosing regimens. Thirteen patients in the study had sarcomas and had received a mean of three prior lines of therapy. Encouraging clinical activity in the sarcoma subset includes: Evidence of clinical activity consistent with a differentiation‑driven mechanism of action, with disease control observed across multiple sarcoma subtypes Disease control rate (DCR) of 54% at 12 weeks , including one confirmed partial response, and a median progression ‑ free survival of 6 months Robust target engagement , demonstrated by an average >50% reduction in m6A (methylated adenosine) marks on mRNA within 24 hours of dosing across dose cohorts Quantitative m6A and transcriptomic analyses providing supportive evidence of downstream effects on gene transcription, including RNA transcript changes associated with STC‑15 treatment In patients who derived clinical benefit, decreased enrichment of genes associated with developmental pathways , consistent with modulation of biological processes linked to cancer stemness and aberrant differentiation, central to sarcoma pathology Taken together, these data provide PD and transcriptional evidence linking METTL3 inhibition to modulation of gene expression pathways relevant to sarcoma biology, supporting the proposed mechanism of action of STC‑15. Justin Moser, Associate Clinical Investigator at HonorHealth Research Institute and Associate Research Professor at Arizona State University John Shufeldt School of Medicine, said: “STC‑15 represents a novel, first-in-class approach to treating sarcoma by targeting RNA methylation to disrupt malignant progression. Early clinical activity, supported by biomarker evidence of target engagement and transcriptional modulation, supports further evaluation in this devastating disease with high mortality and limited treatment options.” Jerry McMahon, Chief Executive Officer of STORM Therapeutics, commented: “These data from the Phase 1 sarcoma subset provide encouraging early clinical and molecular evidence supporting STC‑15’s differentiation‑focused mechanism of action. Importantly, we observed a connection between target engagement, downstream transcriptional effects and signals of clinical benefit. For heavily pretreated sarcoma patients with limited treatment options, these results support our ongoing Phase 2 trial and highlight STC-15’s potential to transcriptionally reprogram tumor cells.” STC-15 represents a novel therapeutic approach in sarcoma by targeting RNA methylation to modulate aberrant epitranscriptomic programs that are central to sarcoma biology. In this Phase 1 sarcoma subset, STC-15 demonstrated robust target engagement with substantial reductions in m6A marks accompanied by downstream transcriptional changes. In patients who derived clinical benefit, these changes were associated with decreased enrichment of genes linked to developmental pathways that lead to cancer cell proliferation, mutation and spread. These findings support the continued clinical evaluation of STC-15 in an ongoing Phase 2 study in selected sarcoma populations, assessing safety, pharmacokinetics, efficacy and exploratory biomarkers. STC-15 is also available to cancer patients under an Expanded Access Program. Details of the poster presentation are as follows: Poster Title: A Subset Analysis of Clinical Activity and Pharmacodynamic Biomarkers in Patients with Sarcomas in the Phase 1 Dose Escalation Study of STC-15, a METTL3 Inhibitor Presenter: Justin C Moser, Associate Clinical Investigator at HonorHealth Research Institute, Scottsdale, AZ Authors: Justin C Moser 1 , Jordi Rodon Ahnert 2 , Kyriakos P. Papadopoulos 3 , Yaara Ofir- Rosenfeld 4 , Josefin-Beate Holz 4 , Melinda Snyder 4 , Marguerite Hutchinson 4 , Kristen McCaleb 4 , Sean Uryu 4 , Ayush Raman 5 , Ananya Anmangandla 5 , Samantha M Carlisle 6 , Audrey Delgarno 6 , Laura Hover 6 , Ian Hoskins 6 , Gudrun Stengel 5 , Eric Martin 4 Session Type/Title: Poster Session - Sarcoma Date and Time: June 1, 2026, 1:30 PM-4:30 PM CDT Location: Hall A - Posters and Exhibits Abstract Number: 11548 Poster Board: 338 Full abstract details can be found on the STORM website here . 1 HonorHealth Research Institute, Scottsdale, AZ; 2 Department of Investigational Cancer Therapeutics (Phase I Clinical Trials Program), The University of Texas MD Anderson Cancer Center, Houston, TX; 3 START San Antonio, San Antonio, TX; 4 Storm Therapeutics Ltd, Cambridge, United Kingdom; 5 Alida Biosciences Inc., San Diego, CA ; 6 Monoceros Biosystems, San Diego, CA . CONTACTS: STORM Therapeutics Ltd Tel: +44 (0)1223 804174 info@stormtherapeutics.com Optimum Strategic Communications Mary Clark, Zoe Bolt, Elena Bates Tel: +44 (0)203 882 9621 storm@optimumcomms.com NOTES TO EDITORS About STORM Therapeutics STORM Therapeutics is a clinical-stage biotechnology company targeting RNA modifications to reprogram malignant cells and treat disease. STORM’s lead candidate, STC-15, is the first RNA-modifying enzyme inhibitor to enter human clinical trials. STC-15 specifically inhibits METTL3, an RNA-modifying enzyme that regulates stem cell transformation and differentiation, a critical process in the development of sarcomas and other tumors. STC-15 is currently being assessed as a monotherapy in a Phase 2 study for select sarcomas. Further information is available at NCT identifier: NCT06975293. For more information, please visit