JAK2 and myeloproliferative neoplasm: To address these issues we investigated the frequency, status, and allelic variation of JAK2 V617F mutation in Korean MPN patients and demonstrated the usefulness of JAK2 V617F mutation as a molecular marker for treatment response and/or disease progression in BCR-ABL-negative MPNs using quantitative real time polymerase chain reaction (qPCR) and pyrosequencing.