We previously reported that a single oral dose of DMBA administered to heterozygous BALB/c Trp53 knockout female mice significantly accelerated induction of ERα-positive mammary carcinomas with frequent Hras mutations at codon 61 (10/10 mice) as compared with BALB/c wild type mice, suggesting the combination of Trp53 gene function deficiency and exogenous factors contributed the increased susceptibility to mammary carcinogenesis (Machida and Imai, 2021). This evidence concerns the gene ESR1 and breast carcinoma.