TP53 Mutation Status of Tubo-ovarian and Peritoneal High-grade Serous Carcinoma with a Wild-type p53 Immunostaining Pattern

Background/Aim: Diffuse and strong nuclear p53 immunoreactivity and a complete lack of p53 expression are regarded as indicative of missense and nonsense mutations, respectively, of the TP53 gene. Tubo-ovarian and peritoneal high-grade serous carcinoma (HGSC) is characterized by aberrant p53 expression induced by a TP53 mutation. However, our experience with some HGSC cases with a wild-type p53 immunostaining pattern led us to comprehensively review previous cases and investigate the TP53 mutational status of the exceptional cases. Materials and Methods: We analyzed the immunophenotype of 153 cases of HGSC and performed TP53 gene sequencing analysis in those with a wild-type p53 immunostaining pattern. Results: Immunostaining revealed that 109 (71.3%) cases displayed diffuse and strong p53 expression (missense mutation pattern), while 39 (25.5%) had no p53 expression (nonsense mutation pattern). The remaining five cases of HGSC showed a wild-type p53 immunostaining pattern. Direct sequencing analysis revealed that three of these cases harbored nonsense TP53 mutations and two had novel splice site deletions. Conclusion: TP53 mutation is almost invariably present in HGSC, and p53 immunostaining can be used as a surrogate marker of TP53 mutation. In cases with a wild-type p53 immunostaining pattern, direct sequencing for TP53 mutational status can be helpful to confirm the presence of a TP53 mutation.