Reclassification of Peritoneal Washings from Gynecologic Oncologic Patients Using The International System For Reporting Serous Fluid Cytopathology

Summary: Introduction: The International System for Reporting Serous Fluid Cytopathology (TIS) classifies serous effusions into five categories: non-diagnostic (ND), negative for malignancy (NFM), atypia of unknown significance (AUS), suspicious for malignancy (SFM), and malignant (MAL). In ovarian borderline tumors (OBT), AUS is contradictory when peritoneal washings (PW) contain neoplastic cells cytologically and immunohistochemically (IHC) consistent with origin from OBT. Furthermore, the College of American Pathologists synoptic reporting does not currently address this issue. This study aimed to reclassify PWs from gynecologic oncologic patients per TIS. Materials and Methods: Retrospective database search identified PWs from patients undergoing oophorectomy and/or hysterectomy. Clinical-pathologic data were collected, including patient age, original cytology diagnosis, IHC stains, diagnosis comment, surgical pathology diagnosis, and pathologic stage. Results: A total of 125 cases were reclassified based on TIS (Table 1, Figure 1). The median patient age was 62 years (18-89). Of 7 cases initially reported as "neoplastic cells present," 1 was upgraded to MAL due to associated ovarian granulosa cell tumor, and the remaining 6 cases, all OBTs (with confirmatory IHC for Mullerian origin), were reclassified as AUS per TIS, resulting in upstaging the OBTs to pT1c3. Most atypical PWs (15/19, 78.9%) were reclassified as AUS, 3 (15.8%) downgraded as NFM, and 1 (5.3%) upgraded as SFM. Of these 15 cases of AUS, inconclusive IHC (12, 80%) predominated, followed by low cellularity (2, 13.3%) and degenerative changes (1, 6.7%). Conclusions: Malignant and negative categories showed 100% concordance between the two reporting systems. Majority (78.9%) of PWs originally reported as atypical were reclassified as AUS. The presence of tumor cells originating from OBTs significantly impacted staging in 4/6 patients. We propose the expansion of TIS diagnostic categories to include a specific designation "neoplastic cells present", enhancing clarity and standardization in reporting PW cytology findings in patients with OBTs.