It is noteworthy that a subset of human solid tumor-derived cell lines exhibit high levels of spontaneous DNA double-strand breaks; these include cell lines that lack p53 (e.g., HCT116p53−/− colon carcinoma; SKOV3 ovarian carcinoma) or p21 (e.g., HCT116p21−/− colon carcinoma), and those expressing mutant p53 (e.g., MDA-MB-231 breast carcinoma) [105]. Here, TP53 is linked to breast carcinoma.