FDA Grants Breakthrough Therapy Designation to Pimicotinib for TGCT

Patients with tenosynovial giant cell tumors, a rare locally aggressive neoplasm, who are unable to undergo surgery may benefit from treatment with pimicotinib.

The FDA has given pimicotinib breakthrough therapy designation for the treatment of patients with tenosynovial giant cell tumors (TGCT), a rare locally aggressive neoplasm of the synovial joints, according to a press release from Abbisko Therapeutics.1

Preliminary findings from a phase 1b trial indicated an overall response rate of 68.0% among patients receiving pimicotinib for a rare locally aggressive neoplasm.

Preliminary findings from a phase 1b trial indicated an overall response rate of 68.0% among patients receiving pimicotinib for a rare locally aggressive neoplasm.

The designation was based on data from a phase 1b clinical trial (NCT04192344) assessing pimicotinib in a cohort of patients with TGCT.

“We are very pleased to learn that the FDA has granted pimicotinib breakthrough therapy designation,” Xu Yao-Chang, PhD, chair and chief executive officer of Abbisko, said in the press release. “It will make our clinical development process and finished drug progress more efficient, which will help shorten the time to market and benefit patients worldwide as soon as possible.”

Pimicotinib is an orally available, high selective and potent CSF-1R small molecule inhibitor. Previous research has indicated that inhibiting the CSF-1R signaling pathway may modulate and alter macrophage functions. As such, CSF-1R inhibitors such as pimicotinib could be a treatment strategy for macrophage-dependent diseases.

Preliminary findings from a phase 1b trial assessing pimicotinib in advanced TGCT identified notable antitumor activity and a well-tolerated safety profile.2 Patients were on treatment for a median duration of 105 days (range, 49-164). Almost all patients remained on treatment (96.3%) and nearly three-fourths (74.0%) were on treatment for 3 months. The preliminary overall response rate was 68.0%.

Investigators reported that there was no apparent hepatic toxicity associated with pimicotinib.

The phase 1b study has an estimated enrollment of 85 patients. Patients on the trial are being treated with oral pimicotinib at a dose of 25 mg once a day using a 3+3 dose escalation strategy.

The primary outcome measure is dose limiting toxicities and incidence/severity of adverse effects. Secondary end points include progression-free survival, duration of response, and disease control rate.

To enroll, patients are required to have histologically confirmed tumors that have progressed on or are intolerant to standard treatment or for whom standard therapy is not available. Patients also need to have an ECOG performance status of 0 to 1, a life expectancy of 3 months or more, and adequate organ and bone marrow function.

Those with a known allergy or hypersensitivity to any component of the agent, an additional malignancy that is progressing or needing treatment, or an inability to take oral medication are not eligible for enrollment.

Pimicotinib also received breakthrough therapy designation from the Center for Drug Evaluation (CDE) of the National Medical Products Administration for those with TGCT that is not eligible for surgery. The CDE gave clearance to proceed with a phase 3 clinical study assessing pimicotinib in patients with TGCT.


  1. Abbisko Therapeutics announces that US FDA has granted breakthrough therapy designation for its CSF-1R inhibitor pimicotinib (ABSK021). News release. Abbisko Therapeutics. January 30, 2023. Accessed January 31, 2023. http://bit.ly/3jk4TXr
  2. Xu H, Li B, Luo Y, et al. Preliminary phase 1b results of ABSK021 for advanced tenosynovial giant cell tumor: significant antitumor activity and favourable safety profile. Presented at CTOS 2022 Annual Meeting; November 16-19, 2022; Vancouver, BC. Abst P164. Accessed January 31, 2023.
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