Pimicotinib Yields 54% Response in Tenosynovial Giant Cell Tumors

The Challenge of Unresectable Tenosynovial Giant Cell Tumors

Tenosynovial giant cell tumors are rare, locally aggressive neoplasms of the joint lining that cause severe pain and functional impairment [1, 2]. While surgical excision remains the standard of care, recurrence rates are high, particularly for the diffuse subtype, leaving many patients with inoperable disease [2]. The pathophysiology is driven by a genetic translocation that overexpresses colony-stimulating factor 1, a signaling protein that recruits a destructive influx of macrophages into the joint [1]. Systemic therapies targeting the colony-stimulating factor 1 receptor have emerged as an alternative to surgery, but earlier drugs in this class are often limited by severe side effects, including significant hepatotoxicity [1, 3]. A recent phase 3 trial now offers fresh insights into pimicotinib, a highly selective oral inhibitor designed to address these dose-limiting toxicities in patients with unresectable tumors [4, 5].

The MANEUVER Trial: Evaluating a Selective Inhibitor

To address the lack of systemic treatment options for inoperable disease, researchers launched the MANEUVER trial to evaluate the efficacy and safety of pimicotinib. This drug is a highly selective, potent colony-stimulating factor-1 receptor inhibitor, a targeted therapy that blocks the specific signaling pathway responsible for macrophage accumulation in the joint. The randomized, placebo-controlled, phase 3 study was conducted across 40 specialized hospitals in Asia, Europe, and North America. Investigators enrolled patients aged 18 years and older with unresectable, symptomatic tenosynovial giant cell tumors. To ensure the clinical relevance of the symptom burden, inclusion required a patient-reported worst stiffness or worst pain score of at least 4 on a scale of 0 to 10. During the first part of the trial, patients were randomly assigned in a 2 to 1 ratio to receive either oral, once-daily pimicotinib 50 mg or a visually identical placebo for 24 weeks. An independent statistician utilized a central interactive web response system to generate the randomization schedule, which included stratification by region (China versus non-China). The trial design also incorporated an open-label extension. All patients who completed the first phase were allowed to continue to an open-label second phase, where placebo-treated patients could cross over to receive pimicotinib for an additional 24 weeks. Eligible patients who completed the second phase were then allowed to continue once-daily pimicotinib long-term. The primary endpoint of the study was the objective response rate at week 25, assessed by a blinded independent review committee using the Response Evaluation Criteria in Solid Tumors version 1.1, the standard radiographic criteria used to measure tumor shrinkage. This efficacy analysis was conducted in the intention-to-treat population, an approach that includes all randomized patients regardless of whether they completed the treatment, thereby reflecting real-world clinical scenarios. Safety was analyzed in patients who received at least one dose of the study drug. For the statistical analysis, missing data were not imputed, and only observed data were analyzed. The ongoing study is registered at ClinicalTrials.gov (NCT05804045) and was funded by Abbisko Therapeutics.

Patient Demographics and Tumor Response Rates

Between April 27, 2023, and March 29, 2024, the researchers screened 126 patients for trial eligibility. Ultimately, 94 patients were randomly assigned to, and received, either pimicotinib (n=63) or placebo (n=31). The randomized cohort demonstrated a broad geographic distribution, including 45 patients from China and 49 patients from non-China regions. Demographically, the study population reflected the typical presentation of tenosynovial giant cell tumors, comprising 64 (68%) female patients and 30 (32%) male patients. The primary efficacy analysis revealed that the objective response rate at week 25 was 54% (34 of 63) in the pimicotinib group, compared to just 3% (one of 31) in the placebo group. This yielded an absolute difference in objective response rate of 51% (95% CI 33 to 63, p<0.0001). Beyond radiographic tumor shrinkage, the researchers noted that pimicotinib showed robust antitumor activity with clinically meaningful improvements in tumor-related functional limitations and symptom burden. For practicing clinicians managing this underserved condition, these findings indicate that pimicotinib could soon provide a highly effective, non-surgical option to preserve joint function and reduce daily pain in patients who are not candidates for resection.

Safety Profile and Hepatic Outcomes

The safety analysis demonstrated that pimicotinib was associated with mainly mild treatment-emergent adverse events. The researchers noted that these consisted of mostly manageable asymptomatic laboratory abnormalities and clinical events, such as pruritus, facial edema, rash, periorbital edema, and fatigue. In contrast, the most common treatment-emergent adverse events in the placebo group were fatigue and arthralgia. When evaluating more severe toxicities, the only grade 3 or 4 treatment-emergent adverse event occurring in more than 10% of pimicotinib-treated patients was an increase in blood creatine phosphokinase, which was documented in eight (13%) of 63 patients. Notably, the study avoided the severe complications that have historically limited this drug class. The investigators confirmed that there was no cholestatic hepatotoxicity, drug-induced liver injury, or hypopigmentation of skin or hair. The absence of severe liver toxicity addresses a major dose-limiting complication seen with older colony-stimulating factor 1 receptor inhibitors, suggesting that patients may not require the intensive, frequent hepatic monitoring mandated by earlier therapies. The clinical tolerability of the medication was further supported by high patient retention and adherence. Throughout the trial, dose reductions occurred in five (8%) of 63 pimicotinib-treated patients. Furthermore, treatment discontinuations occurred in one (2%) of 63 pimicotinib-treated patients, indicating that the adverse event profile rarely necessitated stopping the therapy.

References

1. Humbert P, Vialle C, Chevalerias M, et al. Targeting the colony-stimulating factor 1 axis for the treatment of Tenosynovial Giant Cell Tumors. Cytokine & Growth Factor Reviews. 2025. doi:10.1016/j.cytogfr.2025.10.007

2. Dania V, Stavropoulos NA, Gavriil P, et al. Treatment Modalities for Refractory-Recurrent Tenosynovial Giant Cell Tumor (TGCT): An Update. Medicina. 2024. doi:10.3390/medicina60101675

3. Dou F, Lu D, Gao J. Vimseltinib: A novel colony stimulating factor 1 receptor (CSF1R) inhibitor approved for treatment of tenosynovial giant cell tumors (TGCTs). Intractable & Rare Diseases Research. 2025. doi:10.5582/irdr.2025.01010

4. Xu H, Niu X, Ravi V, et al. Pimicotinib versus placebo for tenosynovial giant cell tumour (MANEUVER): an international, randomised, placebo-controlled, phase 3 trial.. Lancet (London, England). 2026. doi:10.1016/S0140-6736(25)02602-9

5. Niu X, Ravi V, Shan B, et al. MANEUVER: A Phase III study of pimicotinib to assess efficacy and safety in tenosynovial giant cell tumor patients. Future Oncology. 2024. doi:10.1080/14796694.2024.2396227