- The SV40 small t-antigen prevents mammary gland differentiation and induces breast cancer formation in transgenic mice; truncated large T-antigen molecules harboring the intact p53 and pRb binding region do not have this effect. Goetz, F., Tzeng, Y.J., Guhl, E., Merker, J., Graessmann, M., Graessmann, A. Oncogene (2001)