Utility of CD36 as a novel addition to the immunophenotypic signature of RAM-phenotype acute myeloid leukemia and study of its clinicopathological characteristics

Introduction: In 2016, Children Oncology Group (COG) described a new high-risk subtype of acute myeloid leukemia (AML) with a distinct immunophenotypic-signature, RAM-phenotype (RAM-AML). Data on clinical and laboratory features of RAM-AML are still limited to COG report only. Herein, we report the clinicopathological characteristics and detailed immunophenotypic features of RAM-AML patients. In COG report, 38% of RAM-AML belonged to acute megakaryoblastic leukemia (AMKL)-subtype. Hence, we further compared the immunophenotypic features RAM-AML with non-RAM-AMKL diagnosed during the same study period.

Methods: We included RAM-AML and non-RAM AMKL patients diagnosed between January 2017 and December 2019. We studied their morphological, cytochemical, immunophenotyping, cytogenetic, and molecular characteristics. Mean fluorescent intensity (MFI) and expression-pattern of immunophenotypic markers of RAM-AML were compared with non-RAM AMKLs patients.

Results: We identified 11 RAM-AML (1%) and 21 non-RAM AMKL (1.9%) patients in 1102 pediatric-AML patients. Seven of 11 (63.64%) patients belonged to FAB-M7-subtype. CD56, CD117, and CD33 demonstrated overexpression, whereas CD45 and CD38 showed under-expression in RAM-AML patients. CD36 was consistently negative in RAM-AML, whereas moderate-bright positive in non-RAM AMKLs patients (p < 0.0001). On principle component analysis, addition of CD36 enhanced the visual-separation between RAM-AML and non-RAM AMKL clusters. Cytogenetic and molecular studies did not show any recurrent abnormality; however, RNA-sequencing study revealed CBFA2T3-GLIS2-fusion in three of seven (42.8%) RAM-AML patients.

Conclusion: We report the clinicopathological characteristics and the detailed immunophenotypic profile in the world's second series of RAM-AML patients. We further report a novel finding of CD36-negative expression as an additional parameter to the multidimensional immunophenotypic signature of this entity.