Acute Mast Cell Leukemia Preceded by Malignant Mediastinal Germ Cell Tumor: A Case Report and Literature Review.

Background: Mast cell leukemia (MCL) is a highly life-threatening and extremely rare subtype of systemic mastocytosis (SM). MCL often genetically contains one or more somatic mutations, particularly activating mutations of Case Presentation: A 30-year-old Asian male patient who underwent two rounds of surgery and chemotherapy with a history of primary mediastinal GCT (PM-GCTs) was admitted to our hospital due to persistent chest pain and severe fatigue. The diagnosis of acute MCL was confirmed via morphology analysis and chemical staining of marrow aspirate, as well as via marrow biopsy, with the addition of C-findings that included splenomegaly and cytopenia. The atypical MCs were phenotypically positive for CD117 and CD9 but weakly positive for CD2 and negative for CD25. Next-generation sequencing of the marrow aspirate identified heterozygous mutations in Conclusion: In this case, MCL preceded by PM-GCTs had similar clinical symptoms and morphological manifestations but distinctly different genetic profiles than primary MCL. The characteristic morphology of MCL provides the most pivotal evidence that led our diagnosis in the correct direction. A competing hypothesis is that there is a common embryonal cancer stem cell between PM-GCTs and secondary MCL, and the latter is gradually developed in the context of additional "driver mutations".