Based on the low mammary tumor incidence reported in the bulk of the literature (summarized in [17]), the equally low spontaneous mammary tumor incidence in multiparous FVB female mice in our isolated colony [18], the identification of the MMTV-induced Int6 truncation in a pre-neoplastic mammary lesion and the ability of Int6sh to transform cells in culture, we believe these tumors were a direct result of expression of Int6sh. The gene discussed is EIF3E; the disease is breast cancer.