Positives

• In the phase 3 indolent mastocytosis trial, patients on masitinib achieved a cumulative response on itching, flushing, depression, and asthenia at more than double the placebo rate (18.7% vs. 7.4%) PMC.
  
  
• In a phase 2a trial, 56% of patients with cutaneous or systemic mastocytosis achieved an overall clinical response that was sustained beyond 60 weeks PubMed.
  
  

Negatives

• Trial participants most commonly reported diarrhea (11%), rash (6%), and asthenia (6%), with phase 2a patients also reporting edema and nausea each in 44% of subjects PMC.
  
  
• Researchers note response is restricted to a subset of patients, with no reliable predictor (KIT mutation status doesn't correlate) of who will benefit PMC.
  
  

Hurdles & Side Effects

• Masitinib remains unapproved by the FDA for MCAS, so US patients who want access have to enroll in the AB Science phase 2 severe MCAS clinical trial PubMed.
  
  
• A leading mast cell specialist has framed masitinib as a path forward for severe MCAS patients precisely because there are no other clinical trials, underscoring how rare access currently is PMC.