Case Report: Experience of a rare case of primary acute mast cell leukemia with FGFR1 gene rearrangement.

Mast cell leukemia represents the most malignant subtype of systemic mastocytosis, characterized by a dire clinical prognosis. Currently, no standard treatment regimen exists, with allogeneic hematopoietic stem cell transplantation being the sole option that may extend patient survival. Most mastocytosis patients exhibit mutations in the KIT gene. This paper presents a case of mast cell leukemia manifesting primarily as intractable shock and extensive bone destruction. Notably, the patient tested negative for KIT gene mutations but exhibited an FGFR1 gene rearrangement. Initial treatment with venetoclax and azacitidine proved ineffective, prompting a shift to second-line targeted therapy using an FGFR1 inhibitor. This case is the first to report FGFR1 gene rearrangement in a mast cell leukemia patient, offering deeper molecular insights into this highly aggressive disease.