LCK and B-cell chronic lymphocytic leukemia: Whereas CLL cell treatment with dexamethasone induced similar levels of cell death between Lck high and low expressing cases (Fig. 4a), we found that CLL cells expressing low levels of Lck required greater concentrations of fludarabine to achieve 90% cell death (LC90) than did those expressing high levels of Lck (Fig. 4b).