Studies with Diethylstilbestrol (DES) in humans and rodents have resulted in a spectrum of toxic and carcinogenic effects. Previous findings on gene expression profiles following DES treatment showed that p53, p21 and bax was transcriptionally regulated in this model. In the present studies,Reverse Transcriptase in situ Polymerase Chain Reaction and immunohistochemistry techniques for localization and expression of p53, p21 and bax at cellular levels was applied. Animal were housed individually and treated with 500μmole/kg b.w of DES, (ip) once daily up to 4 days. Our results have shown, the expression of p53, p21 and bax mRNA were greater in wild-type compared to p53+/- knockout mice. In addition, p53, p21 and bax mRNA were significantly higher in DES-treated compared to control-vehicle animals. Collectively, similar patterns of expression also were seen in p53 and p21 proteins and scored according to the percentage of positive nuclear staining. Therefore, the combination of p53 and p21 were concluded to be a valuable markers and prognostic for carcinogenesis and progression of endometrial cancer. Citation Format: Mohd Nazil Salleh, Tan Mei Cheng, Thuaibah Hashim, Henkie Isahwan Ahamd Mulyadi Lai, Wan Khairuzzaman Wan Ramli. p53 and p21 mRNA and protein expression in treated synthetic estrogen in mouse transgenic animal model. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr A51.