Immunohistochemical expression of p53 is a helpful surrogate marker in the differential diagnosis of primary ovarian mucinous tumors: a large study of 181 cases of mucinous borderline tumor and carcinoma.

Primary ovarian mucinous tumors represent a group of tumors in which the diagnosis can be difficult in some cases. The most problematic aspect is the distinction between mucinous borderline tumor (MBT) and mucinous carcinoma (MC) with expansile type of invasion. Ancillary markers to help this distinction would be beneficial, but due to the overlapping immunohistochemical and molecular features, no markers are currently widely used in this scenario. However, a recent study showed that the immunohistochemical expression of p53 with a discriminatory cut-off of 30% tumor cells with strong nuclear expression can be used as a surrogate, but this finding has not been validated in an independent series of ovarian mucinous tumors. In our study, we analyzed 181 ovarian mucinous tumors (MBT, MC or equivocal), focusing on the practical significance of p53 expression in differential diagnosis, including assessment of the value of the proposed 30% strong expression cut-off. Of the tumors included in the study, 23/109 (21.1%) cases of MBT, 42/60 (70%) cases of MC, and 8/12 (66.7%) of mucinous tumors classified as equivocal (overlap between MBT and MC) showed an abnormal p53 staining pattern, including cases with expression in ≥ 30% of tumor cells, cases with complete negativity, and cases with abnormal cytoplasmic staining. In conclusion, the results of our study confirm that p53 immunohistochemical staining can be of practical use in the differential diagnosis of ovarian mucinous tumors. Our receiver operating characteristics (ROC) analyses demonstrated that although cut-offs lower than 30% yielded slightly higher overall discriminatory performance, the predefined ≥ 30% threshold provided substantially higher specificity, which is likely more relevant in routine diagnostic practice. In the setting of morphologically equivocal ovarian mucinous tumors, higher specificity may reduce the risk of overdiagnosing MBT as MC, while still identifying a substantial subset of malignant tumors.