In complement to this, MUC1 has been shown to transform rat 3Y1 fibroblasts (Li et al. 2003), and MMTV-MUC1 transgenic mice develop spontaneous mammary tumors, indicating that MUC1 is an oncogene in its own right (Schroeder et al. 2004). The gene discussed is MUC1; the disease is breast cancer.