Pioneer work with the Patched1 heterozygous knock out mice (Ptch1+/–), a well-characterized tumor mouse model in which ionizing radiation exposure dramatically accelerates tumor development in the brain and skin (Pazzaglia et al. 2002; Mancuso et al. 2004), has provided examples of in vivo out-of-field oncogenic radiation responses in the mouse brain. The gene discussed is PTCH1; the disease is neoplasm.