
Increasing data suggest that rituximab may have activity in a variety of uncommon B-cell malignancies. Although earlier preliminary data suggested a high response rate in hairy cell leukemia (HCL) (Thomas et al: Blood 94:705a[abstract 3116], 1999), the complete response rate of 20% in patients who had previously failed cladribine (Leustatin) therapy reported by Nieva et al was considered disappointing (abstract #1535). A more promising approach to patients with refractory HCL is the BL-22 immunotoxin, in which anti-CD22 is linked to a Pseudomonas exotoxin (Kreitman et al: N Engl J Med 345:241-247, 2001). Of 16 patients treated on a phase I study who had failed at least one purine analog, 13 responded, including 11 complete remissions. At a median of 16 months, only three complete responders relapsed and these were successfully reinduced.