Unmasking of Chronic Myelomonocytic Leukemia after Treatment of Chronic Lymphocytic Leukemia with Rituximab

The association of myelodysplastic syndromes with lymphoid malignancies has rarely been reported. To our knowledge, there are only 5 reported cases of chronic lymphocytic leukemia (CLL) and chronic myelomonocytic leukemia (CMML) occurring in the same patient. Herein, we describe the case of an 80-year-old woman diagnosed with CLL. She declined chemotherapy and began weekly rituximab 375 mg/m² intravenously. She initially had a solid partial response to treatment. However, after 2 treatments with rituximab her white blood cell count increased, and a peripheral smear was remarkable for large, cleaved, folded cells, identified as monocytes. The previous bone marrow biopsy was retrieved and restained with an α-naphthol butyl esterase for monocytes. An increased atypical monocytic population was exposed, indicative of an evolving CMML. Her 2 malignancies probably arose from 2 different clones by chance. Treatment was begun with decitabine, but with no response. The patient remains transfusion dependent although relatively asymptomatic on hydroxyurea.