Prognostic value of positive peritoneal cytology in FIGO 2009 stage IA grade 1 endometrioid endometrial cancer.

BACKGROUND: We examined the prognostic value of positive peritoneal cytology (PPC) in International Federation of Gynecology and Obstetrics (FIGO) 2009 stage IA grade 1 endometrioid endometrial cancer. METHODS: This single-institution retrospective cohort study included patients who underwent surgical staging with peritoneal cytology sampling and bilateral pathologic pelvic lymph node evaluation between 1/1/2008 and 8/1/2021. Exclusion criteria included suspicious/atypical cytology, lymphovascular space invasion, lymph node involvement (including isolated tumor cells), synchronous malignancies, no nodal evaluation, or receipt of adjuvant therapy. Patients were stratified by PPC or negative peritoneal cytology (NPC) status. Molecular classification and mutational profiling were available for some tumors. RESULTS: Of 1151 eligible patients, 50 (4 %) had PPC. Median age at surgery was 58 years and was similar between groups (P = 0.59). Depth of myometrial invasion, vaginal tears, age, prior secondary malignancies, and PPC were associated with progression-free survival (PFS) on univariable analysis. Five-year PFS rates were 95.2 % (NPC) and 88.8 % (PPC) (P = 0.02). PPC remained independently associated with worse PFS on multivariable analysis (adjusted HR: 2.63, 95 % CI: 1.19-5.80; P = 0.02), though recurrence was limited in number, with 31 events observed across the entire cohort. Molecular profiling of 216 tumors confirmed all four subtypes; subtype distribution did not correlate with outcomes. Tumors in the PPC group were enriched in ARID1A (82 % vs. 44 %, P = 0.001) mutations. CONCLUSION: PPC appears to be independently associated with worse PFS in low-grade, early-stage endometrial cancer despite excellent overall outcomes and absence of adjuvant therapy. ARID1A mutations may promote peritoneal dissemination in these otherwise low-risk tumors.