Towards standardized categorization of serous effusions: application of the International System for Reporting Serous Fluid Cytopathology diagnostic framework with a special emphasis on borderline ovarian tumors

Borderline ovarian tumors (BOT) in effusion cytology are rare, and to date only limited literature has existed.

The current study used the International System for Reporting Fluid Cytopathology (ISRSFC) criteria to reclassify 321 effusion cytology cases from 302 patients, analyzed diagnostic performance among different positive groups and evaluated the risk of malignancy (ROM). A total of 14 BOTs were included, majority of them were mucinous borderline and these tumors were reclassified into atypia of uncertain significance (AUS) and suspicious for malignancy (SFM) intermediate categories. According to ISRSFC criteria, effusion cases were categorized into five different groups: non-diagnostic (ND), negative for malignancy, AUS, SFM and malignant.

The corresponding overall ROMs were 23.3%, 19.4%, 44%, 87.8% and 100%. Morphologically, mucinous BOTs in effusions presented mostly as acellular mucin, while serous BOTs exhibited mesothelial cells with few atypical cells showing mild to moderate nuclear atypia.

These findings highlight the diagnostic difficulty of BOTs in effusion cytology and the need to apply ISRSFC criteria especially for AUS and SFM grey zone categories for standard reporting and clinical guidance.