ID1 and neoplasm: The observed pattern of drug-induced expression changes of ID proteins in CLL, in which down-regulation was associated with cell death in more drug-sensitive CLLs and up-regulation with cell survival in the more drug-resistant CLLs is consistent with the data showing high ID3 expression in CLLs that were more resistant to spontaneous cell death (Figure 8) and is suggestive of a pro-survival function for the ID proteins in this tumour type.