IDH1 and IDH2 are among the most commonly mutated genes in myeloid neoplasms (MNs). It has been proposed that IDH2 R172 mutations (mR172) define a molecular subtype of acute myeloid leukemia (AML), but the clinicopathologic features of AML with mR172 have not been fully described.
We retrospectively identified and characterized all mR172 MNs with increased blasts in our archive for comparison to a similar number of MNs with IDH2 R140 (mR140) and IDH1 R132 (mR132) mutations (n = 39).
mR172 cases had lower leukocyte counts and bone marrow cellularity than did non-mR172 cases. mR172 MNs often displayed blasts with highly invaginated, cleaved nuclei and typically expressed CD34, HLA-DR, CD117, and CD13 but often with diminished CD33. mR172 cases often had co-occurring mutations in myelodysplasia-associated genes and/or an adverse karyotype. Despite frequent adverse-risk genetic changes, in our cohort mR172 cases had significantly improved overall survival vs non-mR172 cases (P = .01), and we validated that mR172 was associated with improved survival in an independent large data set.
We show that MNs with mR172 represent a morphologically and phenotypically distinct subtype, which in our cohort exhibited relatively favorable survival that is not captured in current AML risk assignment.

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