Cytochemical and immunological characteristics of acute monocytic leukaemia.

Immunological and cytochemical findings are presented from 12 cases of morphologically unequivocal acute monocytic leukaemia (AMoL). The results indicate considerable heterogeneity and three main non-morphological subgroups were identified. The blast cells from half the patients were positive for the presence of both cytoplasmic alpha naphthyl acetate esterase (ANAE) and monocyte-associated membrane determinants whereas the cells from three cases lacked detectable monocytic antigens despite the presence of strong cytochemical ANAE activity. A further three cases expressed monocytic antigens but were cytochemically unreactive for ANAE. These cytochemical results, which were extended by electrophoretic studies of ANAE isoenzymes, suggest that the absence of significant cytoplasmic ANAE activity does not preclude the diagnosis of AMoL and that serum lysozyme estimations may be of value in the recognition of immunocytochemically-atypical cases.