Chronic monocytic leukemia terminating in blastic transformation.

Chronic monocytic leukemia (CMoL) is a rare disorder, closely related to malignant histiocytosis, but a separate entity. The clinical course of the patient described in this case report was characterized by persistent monocytosis without response to cytotoxic therapy, and a large number of infections. On two occasions a clone of cells containing an extra chromosome 20 was observed. The disease terminated in a phase with rapidly increasing numbers of immature monocytoid cells, corresponding to blastic transformation.