PRKDC and cancer: In addition, Prkdc mutations to obtain a severe combined immunodeficient phenotype in many mouse strains (like in all NOD-derived immunodeficient strains such as NSG and NOG) and several rat immunodeficient models6,16 limit the use of irradiation needed in certain models such as in cancer treatments because PRKDC is an enzyme essential in DNA nonhomologous end joining and this generates uncontrolled toxicity in the host tissues.