We describe a patient with
Philadelphia chromosome (Ph)-positive
chronic myelogenous leukemia (CML) who developed an extramedullary
blast crisis in the central nervous system (CNS) and then a subcutaneous
tumor of the neck during treatment with
imatinib mesylate. Administered 400 mg of
imatinib mesylate after the diagnosis of chronic-phase CML, the patient achieved a complete cytogenetic remission 4 months later. However, he developed a mixed myeloid/B-cell
blast crisis with additional karyotype abnormalities only in the CNS during a complete cytogenetic remission in the bone marrow. Several doses of intrathecal
chemotherapy and whole-brain irradiation were effective in treating the
blast crisis in the CNS. After 7 months of complete cytogenetic remission, the patient experienced a subcutaneous
tumor in the right neck. A biopsy of the
tumor revealed a mixed myeloid/T-cell
blast crisis. The cytogenetic analysis showed that the
blast crisis clone in the neck
tumor was different from that of the CNS. An increased dose of
imatinib mesylate was ineffective in treating the neck
tumor. Irradiation to the right neck was therefore undertaken. This case suggests that the development of a clone resistant to
imatinib mesylate is not always detected in the bone marrow and that multiple Ph-positive clones have the potential to become transformed into a
blast crisis.