To identify mechanisms of resistance to HSP90 inhibition, we chose three KRAS mutant cell lines (A549, MDA-MB-231, SW480) that are derived from different cancer types (lung adenocarcinoma, triple-negative breast cancer, colorectal cancer) and exhibit dependence on the expression of mutant KRAS and the HSP90 client protein STK33 [16, 18] (Figure 1A). Here, HSP90AB1 is linked to cancer.