Besides the importance of Hsp90 expression levels, specific conformations of the chaperone have been implicated in cancer versus normal cell sensitivity to Hsp90 inhibitors: Hsp90 was shown to display higher binding affinity for 17-AAG exclusively in cancer cells [30], leading to the formation of 17-AAG-sensitive Hsp90-containing "superchaperone" complexes in malignant cells, whereas normal cells bearing a predominantly uncomplexed Hsp90 are significantly less sensitive to these types of inhibitors [13,30]. This evidence concerns the gene HSP90AB1 and cancer.