Merck KGaA has received approval from the US Food and Drug Administration (FDA) for Pimjetmi (pimicotinib), a new treatment for adults with tenosynovial giant cell tumour (TGCT), a rare condition affecting joints and surrounding tissues. The once-daily oral medicine offers an additional treatment option for patients whose tumours cannot be surgically removed without potentially worsening joint function or causing serious complications.
The approval strengthens Merck KGaA’s growing rare tumour portfolio as the Germany-based pharmaceutical company continues to expand its presence in treatments for uncommon diseases through research and strategic acquisitions.
Pimjetmi Targets Tumour Growth Mechanism
TGCT is a rare, non-malignant tumour that develops in the joints and surrounding tissues. Although it does not spread to other parts of the body, it can cause pain, swelling, joint damage and restricted movement. Surgery remains a treatment option; however, tumours can return, and surgical removal may lead to complications or affect joint function.
The condition is associated with excessive production of colony-stimulating factor 1 (CSF-1), a protein that attracts cells involved in tumour growth. Pimjetmi is a small-molecule drug designed to block the CSF-1 receptor, thereby targeting the biological pathway responsible for tumour development.
Phase 3 Trial Demonstrates Promising Results
The FDA approval was supported by results from a Phase 3 clinical trial, which demonstrated significant improvements among patients receiving pimicotinib. At 25 weeks, the treatment achieved an overall response rate of 56%, compared with just 3% among participants receiving a placebo.
Researchers also reported clinically meaningful and statistically significant improvements in secondary measures, including joint range of motion, physical function and pain. According to Merck KGaA, the findings demonstrate the medicine’s potential to address important treatment needs among people living with TGCT.
Pimjetmi Enters a Competitive Treatment Market
With this approval, Pimjetmi will compete with two other small-molecule CSF-1 inhibitors available for TGCT.
Daiichi Sankyo’s Turalio was the first treatment approved by the FDA for this condition in 2019. However, its label carries a boxed warning for serious liver toxicity, which has also affected its regulatory position in Europe. Ono Pharmaceutical’s Romvimza, developed by Deciphera Pharmaceuticals, received FDA approval in 2025. Although it does not carry a boxed warning, its prescribing information includes precautions concerning potential liver-related risks.
In contrast, Merck reported that its pivotal clinical trial showed Pimjetmi was well tolerated, with no evidence of liver toxicity. Nevertheless, its prescribing information also includes precautions relating to elevated liver enzymes.
Merck Strengthens Its Rare Tumour Portfolio
Pimjetmi adds to Merck KGaA’s expanding portfolio of treatments for rare tumours, supported by a series of strategic acquisitions and licensing agreements.
The company initially secured commercialisation rights to pimicotinib from Shanghai-based Abbisko Therapeutics in 2023, covering Greater China and including an option to obtain rights in other global markets. In March 2025, Merck exercised that option through an additional payment of $85 million.
Merck also expanded its rare tumour portfolio through its $3.9 billion acquisition of SpringWorks Therapeutics in 2025. The acquisition added two FDA-approved treatments for rare tumour conditions to its portfolio. More recently, in October 2026, Merck announced a $1.1 billion agreement to acquire Silence Therapeutics, a biotechnology company developing RNA-based treatments, including a potential therapy for polycythaemia vera, a rare blood cancer.
Pimicotinib had previously received approval in China in December 2025 and subsequently gained regulatory approvals in Canada and Switzerland. Meanwhile, the medicine remains under regulatory review in Europe. As reported by medcitynews.com, the FDA approval of Pimjetmi marks another milestone in Merck KGaA’s strategy to strengthen its rare tumour treatment portfolio and expand options for patients with limited treatment alternatives.