Animal models of breast cancer and murine cell lines, albeit criticized for their relevance to human disease, have shown a cooperative interplay between miR-155 and TGF-β signaling in inducing epithelial-to-mesenchymal transition for more invasive cancer behavior, observed in MMTV-PyMT mice and NMuMG cells (Kong et al. 2008; Johansson et al. 2013). The gene discussed is TGFB1; the disease is breast cancer.