MORPHOLOGICAL AND CYTOCHEMICAL FINDINGS IN 150 CASES OF T-LINEAGE ACUTE LYMPHOBLASTIC-LEUKEMIA IN ADULTS

We evaluated the morphological findings in 150 consecutive cases of T- lineage acute lymphocytic leukaemia (T-ALL). Cytochemistry including P AS staining and acid phosphatase reaction proved of limited value for the diagnosis of ALL. The diagnosis of acute leukaemia was easy to est ablish in most instances. However, in a few cases the leukaemic cells were difficult to recognize as blasts. The nuclei of such cells showed condensed chromatin and nucleoli were lacking, and was encountered pa rticularly in thymic ALL. Basophilic cytoplasm combined with prominent vacuolization suggestive of mature B-ALL (ALL-L3 type), was observed in 16 cases. Other features, however, such as cell size, polymorphism, chromatin structure, sparse cytoplasm or focal positivity for acid ph osphatase, excluded a diagnosis of ALL-L3 in those cases. Distinction from hybrid leukaemia was difficult in 20 cases, because of a low perc entage of peroxidase-positive blasts or other features which suggested a separate myeloid leukaemia component. In nine of these the hybrid n ature of the leukaemia was considered as certain on the basis of morph ology. Seven cases had been diagnosed as biphenotypic with coexpressio n of myeloid and lymphoid markers by immunological techniques. In conc lusion, our analysis showed some serious pitfalls of the morphology in T-ALL, clearly indicating the need for immunological analysis of the leukaemic cells. However, morphology remains an essential component of the diagnostic repertoire, especially when the marrow is difficult to aspirate and in cases with equivocal immunological findings. Furtherm ore, recognition of a separate myeloid leukaemic component in addition to the lymphatic one requires a morphological analysis.