Comprehensive immunophenotypic study of acute myeloid leukemia with KMT2A (MLL) rearrangement in adults: A single-institution experience.

Background: Acute myeloid leukemia (AML) with KMT2A (MLL) rearrangement is known for monocytic or myelomonocytic differentiation, but the full immunophenotypic spectrum and dynamic changes of the immunophenotype in this genetically defined disease have not been systematically studied.

Methods: We reviewed the immunophenotype, karyotype, and mutations at the time of initial diagnosis and relapse of adults with AML with KMT2A rearrangement in our institution between 2007 and 2020.

Results: We identified 102 patients: 44 men and 58 women with a median age of 52 years (range, 18-87). Forty-three patients were considered to be therapy-related. Twenty-four out of 64 patients relapsed from complete remission after induction therapy, 34 had persistent/progressive disease, and 58 patients died with a median overall survival of 17 months. We detected five immunophenotypes: immature monocytic (38%); myelomonocytic (22%); myeloblastic (22%); mature monocytic (10%); and acute promyelocytic (APL)-like (8%). By chromosomal breakpoints, we presumed 11 different partners; t(9;11) (p22;q23)/MLLT3-KMT2A was the most common rearrangement (n = 56, 55%), followed by t(6;11) (q27;q23)/AFDN-KMT2A (n = 13,13%). Patients with t(6;11) (q27;q23)/AFDN-KMT2A preferentially showed a myeloblastic phenotype (p = 0.026). Mutations were detected in 39/64 (61%) cases, and RAS pathway (NRAS/KRAS/PTPN11) was involved in 26/64 (41%) cases. None of the APL-like cases had mutations detected. At the time of disease relapse, 10/24 (42%) showed major immunophenotypic change, and 7/10 cases gained additional cytogenetic and/or molecular alterations.

Conclusion: The immunophenotype of AML with KMT2A rearrangement is more diverse than previously recognized, with a substantial subset showing no evidence of monocytic differentiation. Major immunophenotype change is common at the time of relapse.