Transition from morphologic diagnosis to immunophenotypic diagnosis of acute leukemia—experience of establishing a new flow cytometry laboratory

In this era of targeted therapy, traditional reporting of acute leukemia by morphology using French-American-British (FAB) system of classification has limited uses due to lack of standardization and use in risk stratification. Flow cytometry (FCM), cytogenetics, and molecular testing drive the therapeutic decision. However, the lack of high-end testing at all health care strata leaves a general pathologist in a quandary. This study aimed at documenting the leukemia-associated immunophenotype (LAIP) specific for morphologic (FAB) subclasses of acute leukemia (AL). A retrospective case record-based study was carried out including 100 cases of de novo acute leukemia over 1 year to study the association of FCM immunophenotype profile with morphologic FAB classification of acute leukemia. Fourteen cases (14%) were diagnosed as acute leukemia—unclassified by morphology which were accurately classified by FCM into B cell acute lymphoblastic leukemia (ALL) (6), T cell ALL (3), acute myeloid leukemia (AML) (4), and mixed phenotype acute leukemia (MPAL) (1). FCM also differentiated Pre B cell ALL from Burkitt lymphoma, subclassified T cell ALL into thymic categories, diagnosed MPAL, and identified blasts with monocytic differentiation which were not detected by morphology. Although morphologic FAB diagnosis is still widely used to classify acute leukemia, it is imperative that FCM should be used for accurate leukemia diagnosis.