A rare type of tumor that develops in joints and surrounding tissue now has a new FDA-approved treatment, a Merck KGaA drug that can bring patients an alternative to two drugs that have been the only therapy available for this indication.
The regulatory decision announced after Tuesday’s market close covers the treatment of tenosynovial giant cell tumor (TGCT) in adults for whom surgical removal of tumors could worsen joint function or lead to severe complications. The drug, known in development as pimicotinib, is part of the growing rare tumor portfolio of Darmstadt, Germany-based Merck. The once-daily pill will reach the market under the brand name Pimjetmi.
TGCT is not considered cancer because the tumors it causes do not spread. Without surgical removal, these tumors become painful and disfiguring, impairing movement. Even when the tumors are removed, they can come back. Surgery also comes with complication risks.
TGCT stems from a genetic abnormality that leads to overexpression of colony-stimulating factor 1 (CSF-1), a protein that recruits cells that promote tumor growth. Pimjetmi is a small molecule designed to block the CSF-1 receptor. In the Phase 3 clinical trial that supported the drug’s regulatory submission, results for the study drug at 25 weeks showed a 56% overall response rate compared with 3% for those given a placebo. Results also showed clinically meaningful and statistically significant improvement on secondary goals assessing range of motion, physical function, and pain. Detailed data for the TGCT therapy were presented during the 2025 annual meeting of the American Society of Clinical Oncology.
In the Pimjetmi approval announcement, Danny Bar-Zohar, member of the executive board and CEO of Merck’s healthcare division, said the new product strengthens the company’s leadership position in rare tumors.
“Translating scientific innovation into clinically meaningful advances for people living with rare tumors is a strategic imperative for our company, as we continue our commitment to addressing significant unmet needs,” he said.
Pimjetmi will now compete with two small molecule CSF-1 inhibitors. Daiichi Sankyo’s Turalio was the first TGCT drug, approved by the FDA in 2019. The label for the twice-daily pill carries a black box warning for liver toxicity. That safety risk kept the drug from receiving marketing authorization in Europe.
Ono Pharmaceuticals markets the TGCT drug Romvimza, which came from the 2024 acquisition of Deciphera Pharmaceuticals. The twice-weekly capsule was approved by the FDA last year, Romvimza’s label does not have a black box warning but it does advise against use of the drug by those who have high levels of liver enzymes in their blood due to potential liver risks. The label for Merck’s TGCT drug carries a similar precaution. In Pimjetmi’s pivotal clinical trial, Merck reported the study drug was well tolerated with no evidence of liver toxicity.
Pimjetmi was initially developed by Shanghai-based Abbisko Therapeutics. In 2023, Merck inked a deal securing rights to commercialize the drug in Greater China along with an option for rights in the rest of the world. Last year, Merck paid $85 million to exercise that option.
The drug complements Merck’s other rare tumor assets from business deals. Last year, Merck paid $3.9 billion to acquire SpringWorks Therapeutics, a company with two FDA-approved therapies for rare types of tumors. Last month, Merck struck a $1.1 billion deal to buy Silence Therapeutics, a biotech whose lead asset is a small interfering RNA therapy on track for a pivotal test in polycythemia vera, a rare blood cancer.
Pimicotinib was first approved for TCGT in China late last year. The drug has since landed additional approvals in Canada and Switzerland. It’s still under regulatory review in Europe.
Photo: Waldemarus, Getty Images
