October 22, 2026 — University Hospital Southampton announced on October 21 that its first local patient has enrolled in SELECTmeso1, a clinical trial studying an experimental targeted treatment for people whose mesothelioma has returned after initial therapy. The trial is investigating whether a tumor characteristic called MTAP loss can help identify patients who might benefit from the drug navlimetostat (BMS-986504).
The milestone is patient enrollment—not evidence that the treatment works in mesothelioma. Researchers still need to evaluate how the cancer responds and what side effects occur. Read the University Hospital Southampton announcement dated October 21, 2026.
What is the SELECTmeso1 study testing?
Mesothelioma can recur or progress after chemotherapy or immunotherapy. SELECTmeso1 is a phase II research study for people with relapsed malignant mesothelioma whose tumor testing identifies MTAP loss. Researchers are investigating navlimetostat, an experimental drug designed to exploit a biological vulnerability associated with that genetic finding.
The Southampton team says the trial initially opened in Leicester earlier in 2026. The October 21 announcement concerns the first participant enrolled at Southampton; it does not mean the entire trial began this week. According to the registered study, investigators are measuring disease control at specified intervals, progression-free survival, safety, and tolerability. See the SELECTmeso trial registration (ISRCTN15046526).
Why does MTAP matter?
MTAP is a gene involved in cellular metabolism. Some mesothelioma tumors have lost this gene, a feature that may make them vulnerable to medicines targeting related molecular processes. This is the rationale for studying navlimetostat; it is not proof of clinical benefit. Genetic testing would be needed to establish whether a particular tumor has the characteristic being studied.
What the first Southampton enrollment tells us
The hospital identified its first local participant as a 75-year-old man with pleural mesothelioma who had previously received immunotherapy and chemotherapy. His enrollment highlights the unmet need for additional treatment options when disease returns. It does not predict whether this treatment will benefit him or other participants.
Is similar research available in the United States?
There is a separate U.S. study investigating BMS-986504 with standard-of-care treatment in selected advanced solid tumors, including a cohort for diffuse pleural mesothelioma. The National Cancer Institute lists the phase I study as active and identifies Memorial Sloan Kettering sites in New York and New Jersey. This is not SELECTmeso1; it has its own protocol and eligibility criteria. See the NCI trial record, NCT07532902 and the Memorial Sloan Kettering study listing. Recruitment status and eligibility should be confirmed directly with the study team.
What patients and families should take away
SELECTmeso1 represents a test of personalized treatment based on a tumor biomarker. It is too early to know whether navlimetostat will improve survival or quality of life for people with mesothelioma. Not every patient has MTAP loss or meets trial criteria, and participation carries possible risks and uncertain benefits. Patients can ask their treating oncology team whether tumor molecular testing and clinical trial evaluation are appropriate for their situation.
For broader background, visit our mesothelioma information center and Resource Center. This article is part of our mesothelioma news reporting.
Primary sources
- University Hospital Southampton, October 21, 2026 — enrollment announcement and researcher comments.
- ISRCTN15046526 — SELECTmeso registered study and eligibility framework.
- National Cancer Institute — separate U.S. BMS-986504 study including a pleural mesothelioma cohort.
Editorial note: Reporting current as of October 22, 2026. The UK study and U.S. study are distinct trials. Investigational treatments have not been established as effective for mesothelioma. This article is general information, not medical advice. H&S Research & News Desk is an organizational byline. See our editorial standards.