Micropapillary serous carcinoma of the ovary: An immunohistochemical and mutational analysis of p53

Micropapillary serous carcinoma (MPSC) has recently been described as a distinct ovarian neoplasm that shares histologic features with both serous borderline tumors (SBTs) and typical serous carcinomas of the ovary. To further define the relationship of MPSC to these two neoplasms, we evaluated all three tumor types for expression of the p53 protein and p53 gone mutations. The majority of MPSCs demonstrated positive, but only moderately intense, p53 immunostaining in >50% of the cells, whereas SBTs showed very weak staining in a small number of cells. In contrast, the majority of serous carcinomas displayed diffuse, very intense staining and those that did not stain completely lacked any staining for p53. This pattern of p53 immunostaining in MPSCs can be distinguished from the pattern observed in SBTs and in serous carcinomas. Both the MPSCs and the SBTs lacked p53 mutations in the cases analyzed, whereas all immunopositive serous carcinomas were found to have mutations in p53. In addition, one of the immunonegative cases of serous carcinoma had a frameshift mutation resulting in a truncated protein, providing a likely explanation for the lack of detectable p53 protein. These findings provide support for classifying MPSC as a distinct neoplasm of the ovary and suggest that increased expression of wild-type p53 may play a role in its pathogenesis.