The discrepancy between the in vitro and in vivo response to radiation is readily explained
by the fact that tumors do not exist independently of the host organism; cancer cells grow in
the context of a complex microenvironment composed of stromal cells, vasculature, and
elements of the immune system. As the antitumor effect of radiotherapy depends in part on
the immune system, and myeloid-derived cells in the tumor microenvironment modulate the
immune response to tumors, it follows that understanding the effect of radiation on myeloid …