Interestingly, CLL cells expressing low levels of Lck required higher concentrations of fludarabine in vitro for effective induction of cell death than did CLL cells expressing high levels of Lck, and patients with these cells were less likely to have complete or partial response to this drug than patients with CLL cells expressing high levels of Lck. The gene discussed is LCK; the disease is B-cell chronic lymphocytic leukemia.