Correlation of Cytology Pelvic Washings and Histopathologic Stage of Early (pT1/T2) Disease and Late Stage (pT3) Uterine Serous Carcinoma: Findings from a Single Institution Study

Objective: Uterine Serous Carcinoma (USC) is an aggressive non-endometrioid subtype of endometrial carcinoma, often associated with extra-uterine spread and poor outcomes. Although peritoneal cytology was historically included in FIGO staging to detect occult disease, its prognostic relevance in USC remains uncertain. This study aimed to evaluate the correlation between pelvic washing cytology and final histopathologic stage in patients with serous endometrial carcinoma. Methods: We conducted a retrospective review of 26 patients who underwent hysterectomy at our institution between 2010 and 2020. Pelvic washing cytology was classified as positive (atypical or malignant cells present) or negative, and histopathologic staging followed the CAP protocol. Low-grade disease was defined as pT1–pT2 and high-grade disease as pT3. Fisher’s exact test was used to assess the association between cytology and stage. Results: Positive cytology was more frequent than in Stage 1 or 2 disease (93% vs 64%), but the difference was not significant using the Fischer exact test (p=0.13). Along with this, 7 cases out of 11 were staged as low grade but had positive malignant cells in their pelvic washes. One of the cases is presented as an example. Conclusions: In this cohort, despite the diagnosis of low-grade serous carcinoma (pT1-pT2) in these seven cases, washing cytology revealed the presence of malignant cells suggesting that these are not truly low stage tumours. This conclusion is supported by recent studies that demonstrate that patients with low stage uterine cancers with positive peritoneal cytologies have been found to have significantly lower overall survival rates than patients with low stage tumours with negative peritoneal cytologies. Our findings suggest that larger, multicentre studies with standardized cytology protocols are needed to evaluate staging and risk stratification of low stage uterine cancers with positive cytologic findings.