A 60 year-old male presents with anemia and splenomegaly, along with a markedly elevated WBC count with a high percentage of mature lymphocytes. What is the most likely diagnosis?

The presentation of a 60-year-old male with anemia, splenomegaly, and significantly elevated white blood cell (WBC) count characterized by a high percentage of mature lymphocytes is indicative of chronic lymphocytic leukemia (CLL). CLL predominantly affects older adults and is characterized by the accumulation of functionally incompetent, mature lymphocytes.

Anemia and splenomegaly are common complications of CLL as the disease progresses, due to the infiltration of the bone marrow by malignant lymphocytes and the buildup of leukemic cells in the spleen. The elevated WBC count, particularly with a high lymphocyte component, further supports the diagnosis of CLL, as it is one of the hallmarks of this condition.

In contrast, other conditions listed may present differently. Myelodysplastic syndromes often lead to cytopenias due to ineffective hematopoiesis and do not typically present with the high lymphocyte counts seen in CLL. Acute lymphocytic leukemia typically presents with a higher proportion of immature blast cells rather than mature lymphocytes and is more aggressive, also usually seen in younger populations. Chronic myelogenous leukemia may present with high WBC counts but is usually characterized by a significant presence of myeloid