LAUSR

BACKGROUND To examine the association between malignant peritoneal cytology and survival in women with early-stage endometrioid endometrial cancer. METHODS This is a retrospective cohort study using the Surveillance, Epidemiology, and End Results Program from 2010 to 2016. Women with stage I endometrioid endometrial cancer who had peritoneal cytology testing at hysterectomy were examined (N = 24,800). Characteristics and survival related to malignant peritoneal cytology were assessed. The propensity score inverse probability of treatment weighting was used to balance the measured covariates. FINDINGS Malignant peritoneal cytology was reported in 1081 (4.4%) women. In multivariable analysis, stage IB disease and moderately/poorly differentiated tumours were associated with an increased likelihood of malignant peritoneal cytology (both P < 0.05). In a weighted model, malignant peritoneal cytology was associated with decreased cause-specific survival (5-year rates, 92.1% versus 96.8%, hazard ratio [HR] 1.98, 95% confidence interval [CI] 1.56-2.52) and overall survival (89.4% versus 93.1%, HR 1.41, 95% CI 1.16-1.72). In sensitivity analyses, malignant peritoneal cytology was associated with decreased overall survival in the high-intermediate-risk group (5-year rates, 77.8% versus 83.6%, HR 1.57, 95% CI 1.20-2.06) and decreased cause-specific survival in the low-risk group (95.4% versus 98.0%, HR 1.64, 95% CI 1.01-2.68). In the high-intermediate-risk group with malignant peritoneal cytology, postoperative chemotherapy was associated with improved overall survival compared to whole pelvic radiotherapy (5-year rates, 82.7% versus 64.6%, HR 0.36, 95% CI 0.14-0.96). This association was not observed in negative cytology cases (81.5% versus 79.7%, HR 0.78, 95% CI 0.53-1.14). INTERPRETATION Malignant peritoneal cytology may be associated with decreased survival in stage I endometrioid endometrial cancer.