It is of interest that SW48 is the only cell line in our study expressing wild–type p53; considerable apoptosis was also seen in SW707 (mutant p53 and moderately radiosensitive) at 2 Gy, suggesting that p53 status alone is not a robust marker for radiosensitivity in colorectal cancer, a conclusion that is consistent with at least one clinical study of rectal cancer (Nehls et al, 1999). Here, TP53 is linked to rectal cancer.