FDA Approves Merck KGaA’s Pimjetmi, a New Oral Option for a Rare Joint Tumor

Patients with a rare tumor that forms in the joints and the tissue around them now have a new FDA-approved treatment: a once-daily pill from Merck KGaA that offers an alternative to the two therapies that have long been the only options for this condition.

The approval, announced after Tuesday’s market close, covers adults with tenosynovial giant cell tumor (TGCT) for whom surgically removing the tumors could impair joint function or cause serious complications. The drug, known in development as pimicotinib, adds to the growing rare-tumor portfolio at Darmstadt, Germany-based Merck and will be sold under the brand name Pimjetmi.

TGCT is not classified as a cancer because the tumors do not spread. Left untreated, however, they can become painful and disfiguring and restrict movement. Even after surgical removal, the tumors may return, and the operation itself carries the risk of complications.

The disease arises from a genetic abnormality that causes overexpression of colony-stimulating factor 1 (CSF-1), a protein that draws in cells that fuel tumor growth. Pimjetmi is a small molecule designed to block the CSF-1 receptor. In the Phase 3 trial that supported the regulatory submission, the drug achieved a 56% overall response rate at 25 weeks, compared with 3% for placebo. The study also reported clinically meaningful and statistically significant improvements on secondary measures of range of motion, physical function, and pain. Detailed findings from the trial were presented at the 2025 annual meeting of the American Society of Clinical Oncology.

Danny Bar-Zohar, a member of Merck’s executive board and CEO of its healthcare division, said in the approval announcement that the new product reinforces the company’s leading 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 compete with two other small-molecule CSF-1 inhibitors. Daiichi Sankyo’s Turalio was the first TGCT drug, approved by the FDA in 2019. Its twice-daily label carries a black box warning for liver toxicity, a safety concern that prevented the drug from gaining marketing authorization in Europe.

Ono Pharmaceuticals sells the TGCT drug Romvimza, which it acquired through its 2024 purchase of Deciphera Pharmaceuticals. The twice-weekly capsule won FDA approval last year. Romvimza’s label carries no black box warning but cautions against use in patients with elevated liver enzymes because of potential liver risks, a precaution similar to the one on Merck’s label. In Pimjetmi’s pivotal trial, Merck reported that the drug was well tolerated with no signs of liver toxicity.

Pimjetmi was originally developed by Shanghai-based Abbisko Therapeutics. In 2023, Merck secured rights to commercialize the drug in Greater China, along with an option for rights to the rest of the world, and last year paid $85 million to exercise that option.

The drug rounds out Merck’s other rare-tumor assets built through acquisitions. Last year, the company paid $3.9 billion for SpringWorks Therapeutics, which has two FDA-approved therapies for rare tumors. Last month, it agreed to a $1.1 billion deal for Silence Therapeutics, a biotech whose lead candidate is a small interfering RNA therapy slated for a pivotal trial in polycythemia vera, a rare blood cancer.

Pimicotinib was first approved for TGCT in China late last year and has since won additional approvals in Canada and Switzerland. It remains under regulatory review in Europe.

Photo: Waldemarus, Getty Images

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