The pattern-based interpretation of p53 immunohistochemical expression as a surrogate marker for TP53 mutations in colorectal cancer

Mutations in the TP53 gene, most commonly observed in colorectal cancer (CRC), play an essential role in colorectal carcinogenesis. Although p53 immunohistochemical (IHC) expression patterns have been argued to serve as an excellent surrogate marker for TP53 mutations, its performance has not been confirmed in CRC. We aimed to determine whether p53 IHC expression patterns accurately predict TP53 mutation status as examined by next-generation sequencing (NGS). We performed p53 IHC and sequencing of TP53 by NGS in 92 CRC cases with a microsatellite stable phenotype to investigate the correlation between TP53 mutation status and p53 IHC expression. The concordance between p53 IHC and TP53 mutation was 84/92 (91.3%) overall. However, 6 mutant cases were found in 39 cases with a wild-type IHC pattern. Additionally, there were two discordant cases in which an abnormal p53 IHC pattern (overexpression or cytoplasmic pattern) was found, while NGS detected wild-type p53. Therefore, the optimized p53 IHC performs well and serves as a surrogate test for TP53 mutation in CRC cases. Furthermore, it demonstrates excellent reproducibility between two independent experienced pathologists and may have novel clinical utility for molecular classification algorithms in CRC. We suggest that the four-tier classification of p53 IHC patterns is helpful to evaluate molecular colorectal carcinogenesis.