Malignant histiocytosis occurring in patients with acute lymphocytic leukemia

Five cases of malignant histiocytosis (MH) in patients being treated for acute lymphocytic leukemia (ALL) have been previously reported. Two additional cases are described here, all known cases are reviewed, and the phenomenon is discussed. The most tenable explanation for this phenomenon appears to be that ALL and MH may have been interrelated in these patients with both diseases originating from a common stem cell.