FDA Fast-Tracks New Oral Drug for Debilitating Rare Joint Tumor

BOSTON, MA – January 12, 2026 – Patients suffering from a rare and debilitating joint tumor may soon have a new treatment option, as the U.S. Food and Drug Administration (FDA) has accepted a New Drug Application (NDA) for pimicotinib. EMD Serono, the healthcare business of Merck KGaA, Darmstadt, Germany, announced the regulatory milestone, which moves the once-daily oral therapy a significant step closer to potential approval for patients with tenosynovial giant cell tumor (TGCT).

The application, which has been granted Breakthrough Therapy Designation, is based on compelling results from the global Phase 3 MANEUVER study. The data demonstrated that pimicotinib not only achieved significant tumor reduction but also provided meaningful relief from the painful and disabling symptoms of the disease, addressing a critical unmet need for this patient population.

“With pimicotinib, we have an opportunity to significantly advance care for people living with TGCT, a painful and debilitating disease that has few effective and well-tolerated treatment options beyond surgery,” said David Weinreich, Global Head of R&D and Chief Medical Officer for the Healthcare business of Merck KGaA, Darmstadt, Germany. “We are confident in the important role pimicotinib can play for TGCT patients in the U.S. and worldwide.”

A New Front in Treating a Disabling Condition

Tenosynovial giant cell tumor is a rare, locally aggressive neoplasm that forms in or around joints, most commonly the knee. While not typically metastatic, the tumor's growth can be relentless, leading to progressive swelling, severe pain, stiffness, and significantly reduced mobility. For the often young and otherwise healthy individuals it affects, the impact on daily activities and overall quality of life can be devastating. Studies have shown that over 80% of patients experience pain that affects their daily lives and limitations in their range of motion.

For years, the primary standard of care has been surgical resection. However, for many patients, this is not a permanent solution. The diffuse form of TGCT can be difficult to remove completely, leading to high recurrence rates, estimated between 20% and 50%. Repeated surgeries carry their own risks, including increased morbidity, joint damage, and functional limitations, with amputation being a last resort in severe cases. Furthermore, a subset of patients have tumors considered inoperable or not amenable to improvement with surgery, leaving them with very few options.

This gap in care has created a profound need for effective systemic therapies that can manage the disease long-term, control tumor growth, and, most importantly, restore function and alleviate the burdensome symptoms that define the patient experience.

Unpacking the Clinical Promise of Pimicotinib

The foundation of the FDA submission is the pivotal Phase 3 MANEUVER study, a global trial that evaluated the efficacy and safety of pimicotinib against a placebo. The study successfully met its primary endpoint, showing a statistically significant improvement in the objective response rate (ORR)—a measure of tumor shrinkage—at 25 weeks, as assessed by a blinded independent review committee.

Crucially, the benefits extended beyond tumor size. The trial also demonstrated statistically significant and clinically meaningful improvements across all key secondary endpoints. Patients treated with pimicotinib reported reductions in pain and stiffness and showed measurable gains in physical function and active range of motion. These patient-reported outcomes are vital, as they reflect a tangible improvement in quality of life.

Longer-term data presented at the European Society for Medical Oncology (ESMO) Congress in 2025 further solidified the drug's promise. With a median follow-up of 14.3 months, the objective response rate among patients who received pimicotinib from the start of the study continued to increase over time. This suggests a deep and durable response to the therapy.

Pimicotinib is a novel, highly selective small-molecule inhibitor of the colony-stimulating factor-1 receptor (CSF-1R). In TGCT, the overexpression of the CSF-1 ligand drives the accumulation of inflammatory cells that form the bulk of the tumor. By potently and selectively blocking this pathway, pimicotinib aims to halt the underlying biological driver of the disease.

Navigating a Competitive and Evolving Market

Should it gain approval, pimicotinib will enter an evolving but competitive therapeutic landscape for TGCT. For years, patients without surgical options had no approved systemic therapies. In 2019, the FDA approved pexidartinib (Turalio), the first oral CSF-1R inhibitor for the disease. While effective, its use is limited by a boxed warning for serious and potentially fatal liver injury, requiring a strict risk management program.

More recently, in early 2025, the FDA approved vimseltinib (Romvimza), another oral CSF-1R inhibitor that demonstrated strong efficacy and a more favorable safety profile, notably without the significant liver toxicity concerns associated with its predecessor. Pimicotinib is now poised to become the third approved oral agent in this class.

Its differentiation will likely hinge on its combined profile of efficacy, safety, and convenience. The MANEUVER study's robust data on both tumor response and symptom improvement will be a key factor. Furthermore, its once-daily oral dosing schedule could offer a convenience advantage for patients requiring long-term treatment. Developed by Abbisko Therapeutics and licensed for worldwide commercialization by Merck KGaA, Darmstadt, Germany, pimicotinib represents a strategic addition to the company's oncology portfolio, targeting a clear unmet need in a rare disease market projected to exceed $2 billion by the next decade.

The Path to Approval and Global Ambitions

The FDA's acceptance of the NDA for review marks the beginning of the final regulatory leg in the United States. Pimicotinib's Breakthrough Therapy Designation is intended to expedite the review of drugs for serious conditions where preliminary evidence suggests a substantial improvement over available therapy. This designation often comes with a Priority Review, which would shorten the FDA's review timeline from the standard 10 months to just six.

The U.S. filing is part of a broader global strategy. In December 2025, pimicotinib was approved by China's National Medical Products Administration (NMPA), making it the first systemic therapy for TGCT available in that country. It has also received Priority Medicine (PRIME) designation from the European Medicines Agency, signaling its importance to European regulators.

This global regulatory momentum, born from a successful collaboration between the innovative biotech Abbisko and the global commercial power of Merck KGaA, Darmstadt, Germany, underscores the drug's potential. For thousands of patients grappling with the daily challenges of TGCT, the prospect of a new, effective, and well-tolerated oral therapy offers a powerful sense of hope for a future with less pain and greater mobility.