Treatment results and outcomes vary among patients. The advent of the chemotherapy drug cladribine (Leustatin®) has resulted in approximately an 85 percent rate of complete remission (no evidence of the disease) and approximately 10 percent rate of partial response.

Many patients remain disease free for years or decades after treatment with cladribine or pentostatin (Nipent®) and have a normal life expectancy.

Minimal Residual Disease

Some people with hairy cell leukemia have a very low level of remaining hairy cell leukemia cells after treatment. The remaining hairy cell leukemia cells are called minimal residual disease (MRD). The usual blood and marrow tests can't detect MRD. Your doctor may examine your blood or marrow using extra sensitive molecular tests such as four-color cell flow cytometry and polymerase chain reaction for any remaining cancer cells. Although most patients who have an apparent complete remission have minimal residual hairy cell disease, long-term remissions are common.