A previously healthy 49-year-old man presents with fever and night sweats. He has splenomegaly. His.

A previously healthy 49-year-old man presents with fever and night sweats. He has splenomegaly. His peripheral white blood cell count is 22,000/?L, and a peripheral smear shows immature leukocytes with an increase in the number of basophils. Leukocyte alkaline phosphatase score is low, and vitamin B12 level is elevated.