Development of essential thrombocythemia in a patient treated with interferon alfa and pentostatin for hairy cell leukemia.

A patient is reported who developed essential thrombocythemia after successful treatment for hairy cell leukemia. He was initially treated with interferon alfa and subsequently relapsed within one year of treatment. His diagnosis was reconfirmed and then treated with Pentostatin. Six years after treatment he had a progressive increase in the platelet count and was diagnosed as essential thrombocythemia. Second cancers including various types of hematological malignancy have been reported in patients with hairy cell leukemia treated with chemotherapy or interferon alfa. These malignancies may represent either a new clonal disorder or a complication of drug treatment. This is the first report of a chronic myeloproliferative disorder following successful treatment of hairy cell leukemia.