Final answer:
The Philadelphia chromosome is NOT a characteristic usually associated with hairy cell leukemia.
Step-by-step explanation:
The characteristic NOT usually associated with hairy cell leukemia is the Philadelphia chromosome. Hairy cell leukemia is a rare form of chronic lymphocytic leukemia characterized by the abnormal growth of B cells. The other three options, splenomegaly (enlarged spleen), pancytopenia (low blood cell counts), and lymphadenopathy (enlarged lymph nodes), are commonly seen in patients with hairy cell leukemia.