TP53 and rectal cancer: As the histological manifestations and biological behaviors are similar between rectal cancer and colon cancer and no purely rectal cancer cell lines can be obtained from the American Type Culture Collection (ATCC), we selected three colon cancer cell lines, HCT116 (K-RAS mutation; p53 wild type), HT29 (K-RAS wild type; p53 mutation), and SW480 (K-RAS mutation; p53 mutation) from the ATCC to mimic the rectal cancer environment in vitro [30] and assess whether maintenance BEZ235 can prolong the therapeutic effects of combined RT and BEZ235 in a neoadjuvant setting of rectal cancer.