This limitation of low SGC frequency (25%) vs. a high frequency of mammary tumors in the MMTV-LMW-E-T1; p53+/ model reported here, will be addressed in future studies where we will adopt the hybrid MMTV-Cre-Rosa 26 background mice, which show a reduced frequency of mammary tumors30 and increased SGC frequency. This evidence concerns the gene TP53 and breast cancer.