From the structure–activity relationship (SAR) studies, 6BrCaQ (Figure 1) [37,38] was identified as a very promising C-terminal Hsp90 inhibitor displaying an antiproliferative activity LC50 of 5–50 μM [39,40] against various cancer cell lines (MCF7, MDA MB231, Caco2, IGROV, ISHIKAWA, PC3, and HT29 cells). This evidence concerns the gene HSP90AA1 and cancer.