Months after ending cancer program, Theseus lays off 72% of staff as it considers options

Four months after a safety signal blew Theseus Pharmaceuticals’ quest to develop a gastrointestinal stromal tumor (GIST) treatment off course, the biotech is shrinking its head count by almost three-quarters.

The hefty layoffs form part of a “process exploring strategic alternatives,” Theseus announced in a sparse postmarket release Nov 13. “As part of this process, the company plans to consider a wide range of options with a focus on maximizing shareholder value, including potential sale of assets of the company, a sale of the company, a merger or other strategic action,” it explained.

Among the 72% of employees heading out of the door will be the company’s head of R&D, William Shakespeare, Ph.D., although he will continue to support the biotech in a consulting role until the end of June 2024.

Theseus still has some money to play with as the company ended September with $225.4 million in cash and equivalents.  

Fortune turned against Theseus in July when the biotech reported dose-limiting toxicity from the trial of its GIST treatment that drove the company to stop enrollment and end development, sending its stock down 65%.

Today’s release didn’t provide an update on the remainder of the Massachusetts-based company’s pipeline, but Theseus had continued to sound upbeat about its prospects in an earnings update in August.

At the time, CEO Tim Clackson, Ph.D., said the biotech was “excited to be advancing our pipeline,” which is now headed up by an EGFR inhibitor called THE-349. The company expected to submit a request to the FDA in the fourth quarter for a trial of the therapy in EGFR-mutant non-small cell lung cancer, Clackson said.

The biotech hadn’t given up hope on that failed GIST treatment, either, Clackson said in that update. “Theseus is evaluating next steps for potential plans to explore doses of 9 mg and below in clinical studies in patients with mast cell-driven diseases, such as chronic urticaria,” he added at the time.