Although the magnitude of this siRNA effect only reached statistical significance in the latter (Figure 10D), these data suggest that in this more fludarabine-resistant CLL, in which the overall extent of fludarabine-induced cell death was less than in the three other CLLs, loss of ID protein function demonstrably potentiates the fludarabine cytotoxic response. Here, ID1 is linked to B-cell chronic lymphocytic leukemia.