Avapritinib and corticosteroids in advanced systemic mastocytosis with tumoral CMML and associated thrombocytopenia.

Systemic mastocytosis co-occurring with chronic myelomonocytic leukemia (SM-AHN) presents therapeutic challenges, especially in cases of cytopenia. We present a case of a 76-year-old woman with advanced SM-AHN and thrombocytopenia, who responded to reduced-dose avapritinib combined with dexamethasone. Initial treatment with midostaurin and azacitidine was discontinued due to hematological toxicity. Avapritinib (100 mg/day) initiated but reduced to 50 mg/day due to thrombocytopenia risk, with dexamethasone (20 mg) added for platelet support. Clinical improvement was observed within two weeks, with lymphadenopathy resolution, spleen and liver size reduction, platelet count normalization, and serum tryptase decrease. Avapritinib combined with dexamethasone offers a promising therapeutic strategy for SM-AHN, particularly in thrombocytopenic cases.