Which chronic myeloproliferative disorder is treated with Imatinib mesylate (Gleevec), a drug that inhibits tyrosine kinase?

a. Polycythemia vera
b. Chronic myelogenous leukemia
c. Essential thrombocythemia
d. Primary myelofibrosis

ANS: B
Chronic myelogenous leukemia is effectively treated with Imatinib mesylate. This drug inhibits most of the transforming capability stemming from the tyrosine kinase (P210) activity of the bcr/abl fusion gene. This P210 fusion protein is not found in the other myeloproliferative disorders, so the drug is ineffective in these disorders.