Phenotypic and Ultrastructural Profile of M5 Leukemia Cells in Peripheral Blood and Skin Infiltrate

Abstract

The leukemic cells circulating in the peripheral blood and invading the skin of a patient with type M5 myelomonocytic leukemia were compared using ultrastructural, cytochemical and immunological criteria. Neoplastic cells exhibited more differentiated morphologic features in the skin than in peripheral blood, resembling tissue macrophages. The cytochemical pattern did not show any appreciable difference, whereas the surface antigenic profile was dissimilar. Most circulating leukemic cells were Leu M1+ and Leu M3+, and the percentage of OKM1+ and OKIa-1+ cells varied in two different blood samples examined. Conversely, OKIa-1 monoclonal antibody stained virtually all the leukemic cells infiltrating the skin in the absence of any appreciable reactivity with the other monoclonal antibodies. The phenotype of the malignant cells in the skin did not vary during the clinical course of the disease. These observations suggest that the cutaneous microenvironment is able to induce leukemic cells to mutate their phenotypic features towards a more mature state, or that only relatively differentiated circulating leukemic cells are able to leave the bloodstream and colonize the skin.