Sections of end-stage tumors from each of the four breast cancer mouse models and normal mammary glands were stained for fibroblasts using antibodies against PDGFRβ, αSMA and vimentin; for collagen fibers by Masson Trichrome and for epithelial cells using antibodies against E-cadherin and EpCAM (Fig. 1A). The gene discussed is ACTA1; the disease is breast carcinoma.