CLINICAL TRIALS AND OBSERVATIONS Eradication of minimal residual disease in hairy cell leukemia

Although the nucleoside analogs cladrib-ine and pentostatin produce high re-sponse rates in patients with hairy cell leukemia (HCL), a significant number of patients eventually relapse. Several stud-ies have demonstrated that patients with complete remission (CR) have a longer disease-free survival. Therefore, strate-gies to improve on the initial response to nucleoside analog therapy are likely to be beneficial, at least for a proportion of patients. We have treated 13 patients with newly diagnosed HCL (n 11) or after failure of one prior chemotherapy (n 2) with cladribine (5.6 mg/m2 given intrave-nously over 2 hours daily for 5 days) followed by 8 weekly doses of rituximab (375 mg/m2). All patients achieved a CR and minimal residual disease (MRD) as-sessed by consensus primer polymerase chain reaction (PCR) or flow cytometry was eradicated in 11 (92%) of 12 and in 12 (92%) of 13 of patients, respectively. There was no decline in the absolute CD4 and CD8 lymphocyte number after rituximab. We conclude that eradication of MRD in HCL is possible. Whether this leads to a reduced risk of relapse would need to be evaluated in a larger number of patients and with longer follow-up. Disease char-acteristics may potentially be used to identify patients that are more likely to benefit from such additional therapy