Atypical morphological appearance of acute lymphoblastic leukemia confirmed by immunophenotyping

Despite significant advances in diagnostic techniques for acute leukemia, namely immunophenotyping and molecular biology, morphology remains the first essential examination for detecting leukemia and determining whether it is myeloblastic or lymphoblastic in order total discordance with immunophenotyping data. The aim of this study is to report a case of pre-B ALL with a morphological appearance of blasts with “Cup-like” nuclear invagination most often observed in FLT3, NPM, and CEBPA-type AML. We report the case of a 36-year-old man presenting with a tumor and hemorrhagic syndrome with hyperleukocytosis. The blood smear showed blasts with cup-like nuclear invagination, an appearance classically associated with acute myeloblastic leukemia (AML) with FLT3, NPM1, or CEBPA mutations. However, bone marrow immunophenotyping revealed pre-B acute lymphoblastic leukemia (ALL), confirmed by the expression of CD19, CD10, CD34, and TdT, and the absence of myeloperoxidase.This discrepancy between morphology and immunophenotyping illustrates the importance of not limiting oneself to cytological data. Despite appropriate management, the clinical course was rapidly unfavorable, with early death before specific treatment could be initiated.This case highlights the need to systematically combine morphology, immunophenotyping, and molecular analyses in order to obtain an accurate diagnosis, avoid morphological traps, and guide the therapeutic strategy in acute leukemias.