Merck KGaA just secured an FDA approval for its new once-daily oral colony stimulating factor-1 receptor (CSF-1R) inhibitor, adding to a growing list of regulatory checkmarks around the globe.
The agency has approved pimicotinib, under the commercial moniker Pimjetmi, to treat symptomatic tenosynovial giant cell tumor (TGCT), a rare and non-cancerous, locally aggressive tumor that grows in or around the lining of the joints. Pimjetmi is specifically indicated in adults for whom surgical resection of the tumor would cause functional imitation or severe morbidity.
The FDA decision hinged on Merck KGaA's phase 3 Maneuver trial and follows similar approvals from regulators in China, Canada and Switzerland.
The study pitted Pimjetmi against placebo in systemic therapy-eligible patients who hadn't received prior anti-CSF-1/CSF-1R treatment. Pimjetmi led the trial to hit its primary endpoint, generating a 56% objective response rate (ORR) by 25 weeks. The outcome was a significant improvement over placebo, which charted a 3% ORR. And 41.3% of patients experienced an early onset of Pimjetmi relief, demonstrating an ORR by week 13, Merck KGaA said in a Nov. 10 release.
Pimjetmi also significantly improved patient outcomes across a number of secondary endpoints like improved range of motion, physical functioning and pain.
Merck’s longer-term follow up data from the three-part Maneuver trial was presented at the European Society for Medical Oncology last month and, so far, has not reached the median duration of response. Of the patients that responded at 25 weeks, 77% continued to experience clinical benefit after an additional 12 months of follow-up.
Only one patient on Pimjetmi discontinued the treatment due to a drug-emergent adverse event, and five patients (7.9%) required a dose reduction for that reason, Merck explained. Importantly, the drug showed no evidence of hair or skin hypopigmentation or cholestatic hepatotoxicity, the latter of which has been somewhat of a barrier for Daiichi Sankyo’s TGCT treatment Turalio.
Turalio was approved in 2019 as the first systemic therapy for TGCT, but it carries a boxed warning for liver toxicity and an FDA mandated Risk Evaluation and Mitigation Strategy (REMS). Later market entrant and fellow CSF-1R Romvimza from Ono Pharmaceuticals was approved in 2025, and like Pimjetmi, was able to avoid liver toxicity warnings.
Between Apr. 1 and Sept. 30, Ono reported Romvimza revenues of 8.7 billion Japanese yen ($58 million) at an increase of 215.8% year over year. By comparison, Daiichi's Turalio generated 3 billion yen ($18.8 million) between the first (PDF) and second (PDF) quarters of the Japanese fiscal year ending March 31, 2027.
Meanwhile, Pimjetmi's approval also adds momentum to Merck’s rare tumor ambitions.
“With the approval of Pimjetmi in the U.S., we strengthen our leadership position and growing portfolio in rare tumors and bring real hope to patients and their families,” Danny Bar-Zohar, CEO of Healthcare at Merck KGaA, said in a statement.
Merck’s budding rare tumors franchise has been an exercise in acquisitions. The company initially licensed the right to market Pimjetmi in mainland China from Abbisko Therapeutics in 2023 before taking the $85 million option to secure worldwide commercial rights to the drug in April 2025.
In July of 2025, Merck went on to build out its portfolio with its $3.9 billion buyout of of SpringWorks Therapeutics, adding two approved rare tumor drugs in Ogsiveo for progressing desmoid tumors and Gomekli, a treatment for neurofibromatosis type 1 (NF1) patients who have symptomatic benign tumors that can't be removed with surgery. The deal also added an investigational treatment for Hippo-mutant solid tumors to Merck’s pipeline.