FDA Approves Merck KGaA's Pimjetmi, Third CSF-1R Inhibitor for Tenosynovial Giant Cell Tumor
The U.S. Food and Drug Administration on Nov. 10, 2026, approved Pimjetmi (pimicotinib), a once-daily oral CSF-1R inhibitor from Merck KGaA, Darmstadt, Germany, for adults with symptomatic tenosynovial giant cell tumor (TGCT) for whom surgery could worsen functional limitation or cause severe morbidity. The sponsor of record is EMD Serono, the company's U.S. healthcare business, and the drug was discovered and developed by Shanghai-based Abbisko Therapeutics. The decision makes pimicotinib the third CSF-1R inhibitor cleared in the United States for this rare joint tumor, entering a field where the two earlier entrants differ sharply in dosing and liver safety requirements.
Key developments
- FDA approved Pimjetmi on Nov. 10 at 50 mg taken orally once daily, with or without food, for adults with symptomatic TGCT not well suited to surgery.
- In the phase 3 MANEUVER trial, the overall response rate at week 25 was 56% with pimicotinib versus 3.2% with placebo, as assessed by blinded independent central review.
- Among responders, 91% held their response for at least six months and 77% for at least 12 months, according to the FDA; median duration of response was not reached.
- The application carried Fast Track and Breakthrough Therapy designations and was reviewed under Project Orbis alongside regulators in Australia, Canada, Israel, Switzerland and the United Kingdom.
- The U.S. clearance follows approvals in China in December 2025, Canada in June 2026 and Switzerland in October 2026. Merck has not disclosed a U.S. launch date or price.
Disease and treatment background
TGCT is a group of rare, usually benign tumors that form in the synovial lining of joints, bursae and tendon sheaths. Although the tumors seldom spread, they can grow aggressively into surrounding tissue and cause pain, swelling, stiffness and lasting loss of joint function. The American Association for Cancer Research cites an estimated U.S. incidence of about 1.8 to 4 people per million each year. Merck's announcement notes that the condition typically affects young, otherwise healthy adults and is misdiagnosed in up to half of cases.
Surgery remains the standard approach, but diffuse forms of the disease often recur after resection, and repeated operations on knees, hips or ankles can leave patients worse off. The tumors are driven by overexpression of colony-stimulating factor 1, which recruits the inflammatory cells that make up most of the tumor mass; all three approved drugs block its receptor.
MANEUVER enrolled 94 patients who had not received prior anti-CSF-1 or anti-CSF-1R therapy, randomized 2:1 to pimicotinib (63 patients) or placebo (31 patients) for 24 weeks. Forty-nine patients were enrolled in the United States, Canada and Europe and 45 in China. Beyond tumor shrinkage, the drug produced statistically significant improvements over placebo in range of motion, worst pain and physical functioning. The label carries warnings for hepatotoxicity, embryo-fetal toxicity and increased serum creatinine without a change in kidney function. The most common adverse reactions were pruritus, rash, facial and periorbital edema, fatigue, nausea, headache and peripheral edema.
Industry implications
The approval adds a third option to a small but now crowded therapeutic class. Daiichi Sankyo's Turalio (pexidartinib), approved in 2019 as the first systemic TGCT therapy, carries a boxed warning for serious liver injury and is available only through a restricted distribution program. Vimseltinib, sold as Romvimza by Deciphera Pharmaceuticals, a unit of Ono Pharmaceutical, was approved in February 2025 at 30 mg taken twice weekly after a phase 3 trial of 123 patients showed a 40% response rate at week 25 versus none on placebo.
Cross-trial comparisons are unreliable because the studies used different populations and designs. Still, pimicotinib's once-daily schedule, its reported 56% week-25 response rate and a label without a boxed warning or restricted distribution program give prescribers a clear point of differentiation to weigh. Liver monitoring remains part of the class profile, and the FDA lists hepatotoxicity among the warnings for the new drug.
The decision also continues a pattern of Chinese-originated molecules reaching the U.S. market through licensing to Western partners. Abbisko ran the MANEUVER study, with close to half of its patients enrolled in China, and the FDA accepted the multiregional dataset as the basis for approval.
Competitive and supply chain implications
For Merck, the approval extends a rare tumor franchise that already includes Ogsiveo, the first FDA-approved treatment for adults with progressing desmoid tumors who need systemic therapy. Both drugs target small, specialist-treated populations, where orthopedic oncology and sarcoma centers drive most prescribing.
The commercial structure is defined by a licensing deal. Merck first secured rights to pimicotinib in mainland China, Hong Kong, Macau and Taiwan under a 2023 agreement with Abbisko. In March 2025, after the phase 3 readout, Merck exercised an option for U.S. and rest-of-world rights and agreed to pay Abbisko an $85 million option fee. Royalty and milestone terms were not disclosed. The companies also said they would jointly explore further indications, including chronic graft-versus-host disease, an area where CSF-1R inhibition has already been tested by other developers.
Regional implications
The U.S. decision is the fourth national approval for pimicotinib in about 11 months, following China's National Medical Products Administration, Health Canada and Swissmedic. Because the FDA review ran under Project Orbis, the Australian, Israeli and British regulators had access to the same dossier, and Merck said reviews by other Orbis partners are ongoing. The European Medicines Agency took part as an observer and has granted the drug PRIME designation, though no EU approval has been announced.
China played an unusual role in the program. It was both the drug's first market and the source of nearly half the pivotal trial population, and the FDA stratified randomization by region (China versus non-China).
Credence Research analysis
The approval matters less for its size, since TGCT is a rare disease, than for what it says about how rare oncology products now compete. With three CSF-1R inhibitors on the U.S. market, efficacy alone no longer sets a product apart. Dosing frequency, liver safety, monitoring burden and functional outcomes such as pain and range of motion will decide uptake. Pimicotinib's label, which lacks a boxed warning and a restricted distribution requirement, gives Merck a cleaner starting position than the first entrant, while vimseltinib's twice-weekly dosing remains a convenience counterpoint.
The deal structure is equally instructive. Merck paid an option fee only after phase 3 data were in hand, limiting its exposure to development risk while Abbisko carried the trial. That staged licensing model, applied to a China-originated asset with a multiregional dataset, is likely to be copied by other mid-size pharmaceutical companies looking to fill specialty portfolios without large acquisitions. The near-term test is commercial: launch timing, pricing and payer coverage, none of which Merck has yet disclosed.
What comes next
- Merck is expected to announce U.S. launch timing, pricing and patient access support for Pimjetmi.
- Decisions are pending from remaining Project Orbis partners, including Australia's Therapeutic Goods Administration, the U.K. MHRA and Israel's Ministry of Health.
- A European marketing authorization path remains open, with the drug holding EMA PRIME designation.
- Longer-term follow-up from the MANEUVER open-label extension will add data on durability and long-term liver safety.
- Merck and Abbisko plan to explore additional indications, including chronic graft-versus-host disease.
Sources
- U.S. FDA: FDA approves pimicotinib for symptomatic tenosynovial giant cell tumor
- Merck KGaA, Darmstadt, Germany: FDA Approves PIMJETMI (pimicotinib) for Patients with Tenosynovial Giant Cell Tumor
- Merck KGaA, Darmstadt, Germany: Exercises Option for Commercialization of Pimicotinib
- AACR: CSF1 Receptor Inhibitor Vimseltinib Approved for Tenosynovial Giant Cell Tumor
Image: Merck KGaA headquarters in Darmstadt, Germany, by Tobi Bohn Fotografie via Wikimedia Commons, CC BY-SA 4.0. Cropped and edited by Credence Research.
About the Author
Senior News Editor at Credence Research Inc