Merck KGaA's Pimicotinib Shows Promise in Phase 3 TGCT Trial, Setting Stage for Market Competition

Merck KGaA has unveiled detailed phase 3 data for pimicotinib, its investigational treatment for tenosynovial giant cell tumor (TGCT), a rare and locally aggressive tumor type. The results, set to be presented at the upcoming 2025 American Society of Clinical Oncology (ASCO) annual meeting, demonstrate the drug's efficacy and potentially favorable safety profile, positioning it as a strong contender in the emerging TGCT market.

Trial Results and Clinical Implications

The phase 3 trial of pimicotinib, a CSF-1R inhibitor, met its primary endpoint with an impressive overall response rate. Out of 119 patients, 33 achieved partial responses and one complete response after 25 weeks of treatment. The drug showed rapid efficacy, with 26 patients responding within the first 13 weeks. Notably, the median duration of response had not been reached by the data cutoff, suggesting durable benefits.

Secondary endpoints also yielded positive results. Pimicotinib demonstrated significant improvements in range of motion and physical function compared to placebo. Moreover, 61.9% of patients on the drug experienced a reduction in tumor volume, contrasting sharply with only 3.2% in the placebo group.

Safety Profile and Market Positioning

One of pimicotinib's potential advantages lies in its safety profile. Unlike Daiichi Sankyo's Turalio, which carries a boxed warning for liver toxicity, Merck's trial showed no evidence of cholestatic hepatotoxicity or drug-induced liver injury. This favorable safety data could give pimicotinib an edge in the TGCT market, particularly when compared to Turalio and Ono Pharmaceutical's recently approved Romvimza.

Regulatory Strategy and Market Competition

Danny Bar-Zohar, incoming CEO of Merck's healthcare unit, announced plans to initiate regulatory filings for pimicotinib this year. However, the geographic distribution of trial participants – with nearly half enrolled from Chinese sites and only 22% from U.S. and Canadian sites – may draw scrutiny from the FDA, which has recently emphasized increased U.S. enrollment in clinical trials.

As Merck prepares to enter the TGCT market, it faces competition from established players. Daiichi Sankyo's Turalio, approved in 2019, showed significant improvements in motion, stiffness, and physical function in its phase 3 trial, albeit with a lower overall response rate than pimicotinib. Ono Pharmaceutical's Romvimza, approved in February 2025, lacks the boxed safety warning of Turalio, presenting another strong competitor in the field.