There are two additional reasons to choose this oncogene: (i) Viral vector-mediated delivery of a mutated member of the Ras family (Kras, Hras, or Nras) has been reported to cause mammary tumors in mice and rats swiftly (1, 19, 24); (ii) we wanted to compare our result with the previous Platt et al. (15) report on somatic editing of Kras to generate lung tumors. This evidence concerns the gene HRAS and breast cancer.