Systemic mastocytosis with an associated hematological neoplasm (acute myeloid leukaemia with RUNX1::RUNX1T1 fusion) – A case study

Abstract

Systemic mastocytosis (SM) is a rare blood disorder that can affect multiple body organs. There are some patients of SM with coexpression of hematological neoplasm designated in the World Health Organization classification as SM with an associated hematological neoplasm (SM-AHN). A 13-year-old female was referred for immunophenotyping since blasts were reported in the bone marrow aspirate. On performing flow cytometry, abnormal myeloid blasts (>20%) were obtained on flow cytometry suggestive of acute myeloid leukemia with aberrant expression of CD19. Furthermore, there were increased mast cells abnormally expressing CD25. The aspiration slides reviewed showed atypical mast cells Type I and Type II. Molecular analysis revealed RUNX1::RUNX1T1 fusion as well as KIT D816V mutation. Karyotyping revealed a three-way translocation involving chromosomes 8, 12, and 21 consistent with RUNX1::RUNX1T1 fusion. Fluorescence in situ hybridization (FISH) performed using a dual color dual fusion probe for RUNX1::RUNX1T1 showed atypical abnormal pattern consistent with RUNX1::RUNX1T1 fusion. This rare diagnosis could be reached as a result of a strong correlation between morphology, immunophenotyping, cytogenetics, and molecular analysis, leading to a better treatment plan for the patient.