Temporal patterns of serial intraoperative peritoneal cytology among patients undergoing cup-assisted surgery for endometrial cancer: a single-center observational process-monitoring study

The relationship between uterine manipulation during minimally invasive surgery for endometrial cancer and intraoperative peritoneal tumor-cell shedding remains uncertain. We described serial cytological patterns across predefined operative landmarks without estimating manipulator-specific or irrigation-specific effects. This single-center observational process-monitoring study included patients undergoing laparoscopically initiated surgery between June 2018 and August 2024. Eligibility for the cytology-evaluable cohort required a final diagnosis of primary endometrial cancer and at least one evaluable intraoperative cytology result. The primary analysis included cup-assisted cases; no comparable no-manipulator hysterectomy group was available. Cytology was obtained before cup placement (T0), after hysterectomy (T1), after 1,000 mL sterile-water irrigation and saline-based sampling (T2), and after cumulative 2,000 mL irrigation and repeat sampling (T3). Abnormal cytology comprised suspicious/atypical or positive/malignant findings. Adjacent transitions were assessed with exact McNemar tests; complete trajectories required evaluable T0–T3 data. No cytology values were imputed. Of 163 screened patients, 119 were cytology-evaluable, 113 underwent cup-assisted surgery, and 96 had complete T0–T3 data. Abnormal cytology occurred in 4/96, 6/96, 1/96, and 1/96 patients at T0, T1, T2, and T3, respectively. A T0-negative to T1-abnormal transition occurred in 5/94 patients (5.3%; 95% confidence interval [CI], 1.7–12.0). Five of six T1-abnormal results were suspicious/atypical and one was positive/malignant; all six were negative at T2 (100.0%; 95% CI, 54.1–100.0). The T1-to-T2 comparison included seven discordant pairs (exact McNemar P = 0.125). At the administrative data cutoff of May 1, 2026, 94 of the 119 cytology-evaluable patients (79.0%) had a verifiable last follow-up date, whereas 25 (21.0%) were lost to follow-up; no recurrence was documented among the 94 patients with confirmed follow-up. Serial cytological changes were uncommon, but sparse events, indeterminate findings, incomplete sampling, procedural heterogeneity, absence of appropriate surgical and irrigation controls, and lack of centralized rereview, biological validation, recovered-volume measurement, and irrigation-specific safety assessment limit interpretation. Negative T2 cytology indicates non-detection in one specimen, not biological elimination. These exploratory findings should not guide manipulator use, routine sterile-water irrigation, or operative practice and do not establish safety, cytotoxic efficacy, recurrence prevention, or oncological benefit. Not applicable. This observational intraoperative cytology study did not allocate participants to therapeutic interventions.