Cytopathological assessment is an accurate method for identifying immunophenotypic features and BRCA1/2 mutations of high‐grade serous carcinoma from ascites

High-grade serous carcinoma (HGSC) is the most common and aggressive type of ovarian cancer, and it is often associated with ascites at presentation. The objective of this study was to evaluate the accuracy of cytopathology to identify immunophenotypic features of HGSC and BRCA1/2 mutations from ascites.The study included 45 patients with histologically confirmed primary HGSC and malignant ascites. Immunocytochemistry (ICC) staining for PAX8, WT1, P53, P16, and Ki-67 was performed on cytospins and cytoblocks prepared from ascites. Next-generation sequencing (NGS) was used to detect germline/somatic BRCA1/2 mutations in the ascites. Both ICC and NGS results were compared with immunohistochemistry (IHC) and NGS results from tissue blocks of primary tumor. Cronbach α and χICC/IHC results for PAX8, WT1, P53, and P16 showed good reliability between cytospins, cytoblocks, and tissue blocks (α 0.75), whereas poor reliability and significant differences were observed for Ki-67 between ascites and tissue blocks (α 0.26; p.001 [Kruskal-Wallis]). For germline BRCA1/2 mutations, 100% concordance was confirmed, but only 14% concordance was confirmed for somatic mutations.These results demonstrate that cytopathology is an accurate method for identifying immunophenotypic features of HGSC and detecting germline BRCA1/2 mutations from ascites. However, further investigation is required for assessing the proliferation activity of HGSC in ascites and for detecting somatic BRCA1/2 mutations.