EIF2AK2 and breast neoplasm: PKR−/−, as well as eIF2αS/A mice on FVB/N background were crossed with syngeneic mice expressing an oncogenic variant of rat NEU/HER2 (NEU NDL2-5) from the mouse mammary tumor virus (MMTV) promoter, which was previously shown to induce breast tumors in mice with 100% penetrance19.