My laboratory studies ionizing radiation, both as a carcinogen and a therapeutic. I discovered that radiation activates transforming growth factor β (TGFβ) and that TGFβ mediates DNA damage repair by homologous recombination, non-homologous end-joining and alternative end-joining. TGFβ also regulates the composition of the irradiated tumor microenvironment, particularly immune cell phenotypes. Detailed understanding of how TGFβ contributes to therapeutic response in preclinical models of breast, brain, lung and head and neck cancer has generated new rationales for clinical applications of TGFβ inhibitors.