Introduction/Background High-grade serous cancer (HGSC) is the most common and aggressive type of ovarian cancer, and it is often associated with ascites at presentation. The objective of our research was to evaluate the accuracy of cytopathology to identify immunophenotypic features of HGSC and BRCA1/2 mutations from ascites.

Methodology Forty-five patients with histologically confirmed primary HGSC and malignant ascites were included in our study. 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 the primary tumor. Cronbach α and χ2 statistics, respectively, were used.

Results ICC/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.

Conclusion Our results confirmed 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.

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Abstract #270 Figure 1

WT1, PAX8, P53, P16, Ki67 positive stained tumor cells on ascites cytospins and cell blocks, and tumor tissue blocks (immunhisto/cytochemistry results). 200x magnification.

Disclosures The authors made no disclosures. The study was funded by the Slovenian Research Agency (research program P3–0289).