Acute myelomomocytic leukemia terminating in histiocytic medullary reticulosis: cytochemical, cytogenetic and electron microscopic studies.

A case of acute myelomonocytic leukemia terminating in histiocytic medullary reticulosis is reported. The evolution of a single cellular clone presenting with progressive change of the morphological features of the leukemic cells towards more anaplastic elements endowed with prominent phagocytic properties is suggested on the basis of both cytochemical and chromosomal data. The histiocytic nature of the malignant proliferating cells and platelet phagocytosis has been confirmed by electron microscopic investigation. The main pathogenetic explanations of the evolutionary patterns of the disease are discussed with relation to: a) involvement of a common stem cell giving rise to different proliferative patterns of cells in a multiphasic sequence; b) release of dysplastic platelets and defective erythrocytes with massive sequestration by histioid phagocytic cells; and c) coexistence of two different disorders.