Aberrant Cytoplasmic p53 Expression and Its Correlation with TP53 Mutation Status and Functional Implications in Stage II and III Colorectal Cancer

Introduction: TP53 mutation is frequently observed in colorectal cancer (CRC) and is often linked to associated with immunohistochemical p53 expression patterns. Recent studies have identified cytoplasmic p53 expression in CRC, but its correlation with TP53 mutation domains and functional properties remains unclear. Methods: We evaluated nuclear and cytoplasmic p53 staining patterns in 429 stage II and III CRC samples. TP53 mutation status was assessed using targeted next-generation sequencing. Correlations among cytoplasmic expression, mutation domains, functional properties, and clinicopathological features were analyzed. Results: Cytoplasmic p53 expression was detected in 21 (4.9%) CRCs. All cytoplasmic expressions were accompanied by nuclear staining. TP53 mutations associated with cytoplasmic p53 predominantly involved nonsense mutations within the tetramerization domain (TD, 61.9%) and nuclear localization signals (NLSs, 14.3%). All functionally characterized mutations associated with cytoplasmic p53 exhibit loss-of-function (LOF) without gain-of-function or dominant-negative effects. NLS and TD mutations were significantly associated with BRAF V600E mutation but not with microsatellite instability status. Conclusion: Aberrant cytoplasmic p53 expression in CRC leads to nonsense mutations in the TD and NLS domains of TP53. These mutations exclusively induced LOF characteristics. Cytoplasmic expression patterns differ functionally and molecularly from classical nuclear staining patterns, highlighting the need for novel interpretation criteria for p53 immunostaining.