Tumorous manifestation of hairy cell leukemia after long-term treatment with interferon alpha.

Tumorous-manifestation of hairy cell leukemia in a patient treated with IFNα for 7 years is described. After this time, while the patient still was in hematological remission, a tumorous involvement of the lung by hairy cells developed and was successfully treated by surgery. No differences in the phenotype of hairy cells in the lung tumor, in the bone marrow, or in the blood could be detected.