For instance, it was reported that in human cell lines treated with the chemotherapeutic agent etoposide, hypoxia induces p53 levels in breast cancer MCF7 cells, reduces p53 levels in liver cancer HepG2 cells, but does not affect p53 levels in lung cancer A549 cells under the same hypoxic condition (Cosse et al., 2007). Here, TP53 is linked to breast carcinoma.