These results imply that HER2 antigens alone and in conjunction with MHC class I molecules may be lacking on the surface of CT26/HER2-A1 and CT26/HER2-A2 cells, which might be responsible for the lack of IFN-γ induction from immune cells as well as the lack of tumor control in HER2 vaccine-immunized mice. This evidence concerns the gene ERBB2 and neoplasm.