TP53 and breast cancer: Our previous studies have shown that, at the RNA level, a high Δ40p53:p53 ratio is significantly associated with worse disease-free survival in breast cancer [6, 11], and that at the protein level, Δ40p53 is expressed in a subpopulation of cells within the microenvironment of invasive ductal carcinomas (IDCs) [25] and breast cancer cell lines [20].