Molecular Discordance between Myeloid Sarcomas and Concurrent Bone Marrows Occurs in Actionable Genes and Is Associated with Worse Overall Survival

Myeloid sarcoma is a rare, architecture-effacing proliferation of myeloid blasts localized to an extramedullary site, with or without concurrent bone marrow involvement. Clonal heterogeneity results from acquisition of somatic mutations within different subclones of leukemic cells. It was hypothesized that clonal heterogeneity between myeloid sarcomas and concurrent bone marrow biopsies might be present, given their differing biological features and microenvironment. High-throughput sequencing of the largest series (n = 24) of paired myeloid sarcomas and bone marrow biopsies was performed. One third of myeloid sarcomas (8/24) showed discordant molecular profiles, and 75% (n = 6) of these cases had discordant mutations in genes with prognostic significance or molecularly targeted therapies. Patients with molecularly discordant myeloid sarcoma had significantly worse overall survival (median survival, 195 days versus not reached, hazard ratio, 3.3, P < 0.05). Further investigation into molecular discordance between myeloid sarcoma and concurrent bone marrow biopsies may help in understanding clonal evolution of myeloid neoplasms and mechanisms regulating extramedullary blast localization.