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 late-stage 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 Efficacy

The phase 3 trial of pimicotinib, a CSF-1R inhibitor, met its primary endpoint with an impressive response rate. Of the participants, 33 patients achieved partial responses, and one patient showed a complete response after 25 weeks of treatment. The drug's effects were observed rapidly, with 26 patients responding to therapy within just 13 weeks.

Notably, 61.9% of patients receiving pimicotinib experienced a reduction in tumor volume, compared to only 3.2% in the placebo group. The trial also demonstrated significant improvements in patients' range of motion and physical function, addressing key symptomatic concerns associated with TGCT.

Safety Profile and Market Positioning

Merck's pimicotinib appears to have a potential advantage in terms of safety and tolerability. Unlike Daiichi Sankyo's Turalio, which carries a boxed warning for liver toxicity, Merck reported no evidence of cholestatic hepatotoxicity or drug-induced liver injury in its phase 3 trial. This safety profile could be a crucial differentiator as pimicotinib enters a market that includes 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 face scrutiny from the FDA, which has recently emphasized increased U.S. enrollment in clinical trials.

As Merck prepares to enter the TGCT market, it will face competition from established players. Daiichi Sankyo's Turalio, approved by the FDA in 2019, has shown significant improvements in motion, stiffness, and physical function in its own phase 3 trial. However, Turalio's trial had a lower overall response rate and missed its secondary pain endpoint compared to pimicotinib's results.