Isolated Bone Marrow Non–Langerhans Cell Histiocytosis Preceding RUNX1-Mutated Acute Myeloid Leukemia: Case Report and Literature Review

OBJECTIVES: The prevalence of concomitant myeloid neoplasms was recently reported to be unexpectedly high among adults without non-Langerhans cell histiocytosis (non-LCH); however, the coexistence of non-LCH with RUNX1 genetic aberration has not been reported previously. METHODS: Herein, we report a 23-year-old woman with severe pancytopenia diagnosed with non-LCH following presentation with pancytopenia and marrow examination showing histiocytosis positive for CD45, CD68, CD136, and lysozyme but negative for CD1a, langerin, and S100. RESULTS: Whole-exome sequencing showed RUNX1 mutation and NF1 mutation. In the ensuing 6 months, she developed hepatosplenomegaly, and repeat bone marrow evaluation was diagnostic of acute myeloid leukemia (AML). Repeat mutational analysis showed again presence of RUNX1 mutation. She underwent induction therapy but died of septic shock. CONCLUSIONS: The demonstration of RUNX1 mutation in both non-LCH and AML bone marrow specimens at differing time points is suggestive of a biologic association of both distinct disease entities.