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Background The morphological classification of high-risk endometrial cancer is of limited prognostic value. Recent attempts to stratify tumours according to molecular signatures have shown considerable promise. Here we attempted to further refine molecular classifications using markers of the p53 pathway. Methods We analysed the expression of p53 as well as three downstream markers of the p53 pathway, p21, mdm2 and phospho-p63 ( p p63), by immunohistochemistry in a series of 114 endometrial cancers (86 endometrioid, 28 non-endometrioid subtype) with high-risk features (such as high tumour grade and deep myometrial invasion) and correlated results with clinical outcome. The Cancer Genome Atlas (TCGA) data were used to analyse TP63 mutations and copy-number alterations using cBioPortal. TP53 was silenced in two endometrial cancer cell lines to study its effect on p21 and p63. Results About half of the tumours showed a p53 mutant phenotype and there was a strong negative correlation with p21 expression. Being marker positive for p p63 or mdm2 was associated with a significantly increased likelihood of dying, [hazard ratios 5.93 (95% CI 2.37–7.27) and 7.48 (95% CI 3.04–9.39), respectively]. These findings were seen in both p53 wildtype and p53 mutant tumours. Only 11% of TCGA endometrial cancers had a functional TP63 alteration. Upon silencing of TP53, p21 expression was decreased in one cell line, but no effects on p63 were observed. Conclusion Markers of the p53 pathway improve stratification of endometrial cancers and provide novel insights into the role of this pathway in the disease. [ABSTRACT FROM AUTHOR]