NEW ORLEANS-Hairy cell leukemia (HCL) has the highest reported surface expression of CD20 of leukemias studied to date, according to research reviewed at the ASH meeting. In a symposium presentation, Deborah A. Thomas, MD, and colleagues from the M.D. Anderson Cancer Center in Houston, reported that the anti-CD20 monoclonal antibody rituximab (Rituxan) is active against HCL. Response appears to correlate with a decrease in serum interleukin-2 (IL-2) receptor levels. In a poster presentation, Robert J. Kreitman, MD, and colleagues from the National Cancer Institute reported that recombinant immunotoxins containing truncated Pseudomonas exotoxin and targeting either CD25 or CD22 can induce some major responses in patients with refractory HCL.