We next investigated the role of ColXVIII in BC in vivo by crossing our Col18a1 mouse models (Figure 4A) with the transgenic mouse mammary tumor virus–polyoma virus middle T antigen (MMTV-PyMT) mammary carcinogenesis model that recapitulates histological and molecular progression of human ductal BC, including upregulation of ErbB2 (23, 24). The gene discussed is COL18A1; the disease is breast cancer.