Acute Myeloid Leukemias M2, Potentially Misdiagnosed as M3 Variant French-American-Britain (FAB) Subtype: A Transitional Form?

Abstract

From 1990 to 1994, 3 patients with de novo acute myeloid leukemia (AML) in whom light microscopy and cytochemistry suggested a FAB subtype M3 variant were observed at our Institute. Immunophenotype showed HLA-DR⁻, CD13⁺. CD33⁺, CD2⁺, CD9⁺; promyelocytic features were also detected by electron microscopy. However, leukemic cells lacked both translocation t(15;17) and RARα/PML genes rearrangement. These cases were considered to be ‘M2 atypical’ subtypes and they contribute to point out how cytogenetics and molecular biology are mandatory for a correct diagnosis of acute promyelocytic leukemia (APL) particularly because therapy with all trans retinoic acid (ATRA) is now the best treatment for APL. Nevertheless these 3 cases indicate that the atypical M2 subtype may be confused with the M3v if only cytochemistry, immunophenotype and electron microscopy an: used in the defining the FAB subtypes.

Key Words:

• AML M2
• AML M3
• AML Subtype M2