Pimicotinib Demonstrates Best-in-Class Potential with Significant Efficacy and Clinically Meaningful Improvements in Patients with Tenosynovial Giant Cell Tumor

Merck, a leading science and technology company, today announced the presentation of detailed positive results from Part 1 of the global Phase 3 MANEUVER trial evaluating pimicotinib, a potentially best-in-class investigational colony stimulating factor-1 receptor (CSF-1R) inhibitor in development by Abbisko Therapeutics Co., Ltd., in the treatment of patients with tenosynovial giant cell tumor (TGCT). Once-daily pimicotinib demonstrated a statistically significant improvement in the primary endpoint of objective response rate (ORR) assessed by blinded independent review committee (BIRC) compared with placebo at week 25 (54.0% vs. 3.2% for placebo (p<0.0001). The study also demonstrated statistically significant and clinically meaningful improvements in all secondary endpoints related to key patient-reported outcomes in TGCT. These findings will be presented Sunday, June 1 in an oral presentation at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract #11500).

“The impact that TGCT has on patients goes far beyond the physical presence of the tumor. It affects their ability to work, to move freely, and to engage in everyday activities," said Prof. Niu Xiaohui, Director of the Bone and Soft Tissue Tumour Diagnosis and Research Centre at Beijing Jishuitan Hospital. “In MANEUVER, we observed the highest ORR seen to date with a systemic therapy, together with statistically significant improvements in measures of pain, stiffness, and range of motion. These improvements in outcomes that matter to patients with TGCT and the physicians who care for them show the potential of pimicotinib to allow patients to go about their daily lives with fewer negative effects of their disease.”

In MANEUVER, which enrolled patients from China, Europe and North America, the effect of pimicotinib had an early onset, with 41.3 % (26 of 63) of patients experiencing objective response to therapy after 13 weeks. By the data cutoff for primary analysis, nearly all patients in the pimicotinib group (58 of 63 patients; 92.1%) had a decrease in tumor size per BIRC based on RECIST v1.1; one patient achieved a complete response and 33 patients achieved a partial response. The median duration of response was not reached by the data cutoff. The analysis of tumor volume score (TVS, an endpoint designed specifically for TGCT) showed that nearly two-thirds of patients treated with pimicotinib experienced a reduction in tumor volume of at least 50% (61.9% vs. 3.2% for placebo, p<0.0001).

Pimicotinib also demonstrated statistically significant and clinically meaningful improvement across all additional secondary endpoints relevant to patients’ daily lives, and these improvements were seen regardless of achieving objective tumor response to pimicotinib. Pimicotinib improved active range of motion (p=0.0003) and physical function measured by PROMIS-PF scale (p=0.0074). Pimicotinib also reduced worst stiffness (p<0.0001) and worst pain (p<0.0001).

“TGCT, although rare, has a significant impact on the daily lives of the primarily working-age adults who live with the disease, due to swelling, pain, stiffness, and limited mobility caused by the growth of these tumors in and around the joints,” said Danny Bar-Zohar, appointed CEO Healthcare and current Global Head of R&D and Chief Medical Officer. “The landmark global Phase 3 MANEUVER study data will help redefine how TGCT is treated, and we plan regulatory submissions to start this year.”

Pimicotinib was well-tolerated, and the safety profile was consistent with previously reported data, with no evidence of cholestatic hepatotoxicity or hair/skin hypopigmentation. Treatment-emergent adverse events (TEAEs) leading to treatment discontinuation occurred in one patient (1.6%) treated with pimicotinib; TEAEs leading to dose reduction occurred in 7.9% (n=5) of pimicotinib-treated patients.

About MANEUVER

The pivotal Phase 3 MANEUVER study is a three-part, randomized, double-blind, placebo-controlled study to assess the efficacy and safety of pimicotinib in patients with TGCT who require systemic therapy and have not received prior anti-CSF-1/CSF-1R therapy. The study is being conducted by Abbisko Therapeutics in China (n=45), Europe (n=28), and the US and Canada (n=21).

In the double-blind Part 1, 94 patients were randomized 2:1 to receive either 50 mg QD of pimicotinib (n=63) or placebo (n=31) for 24 weeks. The primary endpoint is objective response rate (ORR) at week 25, as measured by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 by blinded independent central review in the intent-to-treat (ITT) population. Secondary endpoints include tumor volume score, active range of motion, stiffness by Numeric Rating Scale (NRS), pain by Brief Pain Inventory (BPI), and physical function measured by Patient-Reported Outcomes Measurement Information System (PROMIS).

After the double-blind Part 1, eligible patients could continue to the open-label Part 2 for up to 24 weeks of dosing, results of which are expected in mid-2025. Patients who complete Part 2 may then enter the open-label extension phase (Part 3) for extended treatment and safety follow-up.

About Pimicotinib (ABSK021)

Pimicotinib (ABSK021), which is being developed by Abbisko Therapeutics, is a novel, orally administered, highly selective and potent small-molecule inhibitor of CSF-1R. Pimicotinib was recently granted Priority Review by the Center for Drug Evaluation (CDE) of the China National Medical Products Administration (NMPA) for the treatment of patients with tenosynovial giant cell tumor (TGCT) who require systemic therapy. Pimicotinib has been granted breakthrough therapy designation (BTD) for the treatment of unresectable TGCT by China National Medical Products Administration (NMPA) and the US Food and Drug Administration (FDA), and priority medicine (PRIME) designation from the European Medicines Agency (EMA). Merck holds worldwide commercialization rights for pimicotinib.

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