Acute myelomonocytic leukemia presenting as a primary cutaneous lymphoma of true histiocytes

Malignant histiocytic and monocytic infiltrates of the skin are seen in true histiocytic lymphomas, in malignant histiocytosis, and in monocytic leukemias. Occasionally such cutaneous lesions constitute the presenting manifestation of the underlying malignancy. We report here a patient whose first manifestation of acute myelomonocytic leukemia was a malignant histiocytic infiltrate in the skin. Cytochemical and electron microscopic data confirmed the histiocytic nature of the skin tumor, and cytochemical data documented the myelomonocytic nature of the subsequent leukemia. Purely histiocytic skin tumors do not often presage myelomonocytic leukemias, although they have developed into monocytic leukemias, and monocytic leukemias have been transformed into myelomonocytic leukemias.