Mutant p53 gain-of-function (GOF) phenotypes have been described in different tissues (Lang et al. 2004; Olive et al. 2004) and helped uncover potential targetable vulnerabilities in p53 mutant breast cancer (Freed-Pastor et al. 2012) and pancreatic ductal adenocarcinoma (PDAC) (Weissmueller et al. 2014). This evidence concerns the gene TP53 and breast cancer.