Merck KGaA has shown off data that fueled its $85 million bet on a late-phase treatment for a rare, locally aggressive tumor. The update provides a closer look at the hand Merck is holding as it gears up to fight Daiichi Sankyo and Ono Pharmaceutical for the tenosynovial giant cell tumor (TGCT) market.
The German drugmaker shared top-line phase 3 data on the CSF-1R inhibitor pimicotinib in TGCT late last year. After seeing the data, Merck paid Abbisko Therapeutics $85 million to take up its option on a global license to the drug candidate. Merck paid Abbisko $70 million for rights to pimicotinib in greater China in 2023.
May 28, Merck shared more phase 3 data ahead of its presentation at the 2025 American Society of Clinical Oncology (ASCO) annual meeting that starts later this week. The drugmaker included data on the primary response rate endpoint and secondary goals that looked at stiffness and pain in its top-line readout last year.
Merck’s latest update sheds light on the speed and durability of the response. The drug worked quickly, with 26 patients responding to therapy after 13 weeks. The primary endpoint, which was assessed after 25 weeks, included 33 partial responses and one complete response. The median duration of response wasn’t reached by the data cutoff.
Merck said 61.9% of patients on pimicotinib had a reduction in tumor volume on an endpoint designed for TGCT, compared to 3.2% of people on placebo. People on the study drug also experienced significant changes in their range of motion and physical function. The data complete a clean sweep of secondary endpoints that included the earlier readout of assessments of stiffness and pain.
These types of noncancerous tumors don't spread to other parts of the body but can be locally aggressive and cause the affected synovium, bursae or tendon sheaths to thicken and overgrow. This, in turn, can cause damage to the surrounding tissue and structures of the affected limb. Symptoms can include pain and swelling while also limiting movement at the joint.
Daiichi’s phase 3 TGCT trial of Turalio, which won FDA approval in 2019, linked the CSF-1R inhibitor to significant improvements in motion, stiffness and physical function. The Japanese drugmaker also had a higher proportion of complete responders than Merck. Yet, Daiichi’s trial had a lower overall response rate and missed its secondary pain endpoint.
Merck also has a potential safety and tolerability advantage. Turalio carries a boxed warning for liver toxicity. Merck saw no evidence of cholestatic hepatotoxicity or drug-induced liver injury in its phase 3 trial. Ono’s Romvimza, which won FDA approval in February, is free from the boxed safety warning and risk-mitigation measures that apply to Turalio.
Danny Bar-Zohar, who is set to become CEO of Merck’s healthcare unit next week, said in a statement that the company will start regulatory filings this year. The FDA’s reaction to the geographic mix is one outstanding question. Chinese sites enrolled almost half the patients. U.S. and Canadian sites collectively enrolled 22% of the patients. The FDA’s cancer unit recently made increased U.S enrollment a focus.