Researchers from Berlin, Germany and Beirut, Lebanon have confirmed in a prospective, observational study that patients with uncontrolled symptoms of indolent systemic mastocytosis (ISM) can improve disease control and their quality of life with the use of avapritinib. Avapritinib is a KIT D816V inhibitor that received approval for use in ISM in May 2023.
A total of 17 patients with uncontrolled ISM were enrolled in the study (median age, 55 years; 60% female) as of October 2024. Lack of symptom control was defined as having a mastocytosis control test (MCT) score of less than 13.
The researchers noted that 100% of the enrolled patients had skin involvement, 47% had osteoporosis, and 20% splenomegaly. Furthermore, anaphylaxis was reported in 40% of patients. Symptom severity, disease control, mastocytosis-quality of life (MC-QoL) score, and disease burden were analyzed at baseline (week 0) and at treatment weeks 4, 12, and 24.
All patients were treated with avapritinib 25 mg/day. Treatment was well tolerated in all but two patients (12%). Quality of life was significantly improved as median MC-QoL scores declined from 61 at baseline to 33 after 4 weeks of treatment (P < .001) and to 17 by 24 weeks. Median MCT score increased from 7 to 15 by week 4 (P< .001). A median MCT score of 16 was achieved at week 24, confirming that disease control was achieved by the overall patient population.
At baseline, the patient population had a median basal serum tryptase concentration of 53 ng/mL. The researchers reported a decrease in this value to 42 ng/mL at treatment week 4, dropping to 6 ng/mL at week 24 (P < .001). Every patient noted that skin involvement continued to improve, including decreasing numbers of lesions, a lesser color intensity of the remaining lesions, and no further episodes of skin flushing.
In conclusion, this real-world, observational study found that patients with ISM who were treated with avapritinib 25 mg daily experienced significant improvement in their quality of life, disease control, and serum tryptase levels, starting as early as 4 weeks after treatment initiation.