Central Nervous System Blast Crisis in Chronic Myeloid Leukemia on Imatinib Mesylate Therapy: Report of Two Cases

Chronic myeloid leukaemia is a chronic myeloproliferative disorder characterised by a reciprocal translocation between chromosomes 9 and 22 and thereby formation of the Philadelphia chromosome. Imatinib mesylate (STI-571) is a potent and selective inhibitor of BCR-ABL tyrosine kinase and has emerged as a treatment of choice in chronic myeloid leukaemia (CML) patients in chronic phase. It has shown activity in CML patients in the chronic phase or blastic phase. However there is poor penetration of the central nervous system (CNS) by the drug or its active metabolites. Therefore the CNS acts as a sanctuary site for malignant cells for CML patients treated with Imatinib. We report cases of two CML patients on Imatinib therapy, who were in haematological remission but developed CNS disease.