RAD21 and neoplasm: Our finding that SI crypt cells and long-lived hematopoietic cells of Rad21+/− mutant animals are more susceptible to killing by radiation raises the possibility that targeted depletion of Rad21 in tumors would be of therapeutic utility and that the level of differential depletion between normal adjacent tissue and tumor cells would not need to be absolute to achieve a clinically relevant differential tumor cell kill.