Eosinophilia during fludarabine treatment of chronic lymphocytic leukemia

Although eosinophilia has been reported as a side effect of purine analogues, there is no report on fludarabine-induced eosinophilia in chronic lymphocytic leukemia (CLL). During chemotherapy with fludarabine and cyclophosphamide, we observed two cases of significant eosinophilia. A 67-year-old patient with CLL developed bone marrow and peripheral blood eosinophilia up to 7.9x10(9)/l, the highest eosinophil count ever reported during treatment with a purine analogue. The eosinophilia persisted for 33 days. Another patient developed bone marrow eosinophilia without eosinophilia in the peripheral blood. These are the first documented cases of fludarabine-induced eosinophilia in CLL, and this side effect may conceivably be more common than previously recognized.