Objective To assess clinicopathologic features and survival outcomes of patients with endometrial carcinoma involving adnexal, full-thickness serosal, or combined involvement.

Methods This international, multi-institutional, retrospective study examined patients with 2009 International Federation of Gynecology and Obstetrics (FIGO) stage IIIA endometrial cancer and tumors involving the uterine serosa and/or adnexa, who were surgically staged between 2000 and 2019. Patients with sarcoma histology, concurrent endometrial/ovarian malignancy, neoadjuvant treatment, positive lymph nodes, or peritoneal disease were excluded.

Results Of 185 patients identified, 139 had tumors with adnexal-only, 40 with serosal-only, and six with combined adnexal/serosal involvement. Median age at diagnosis was 60 years (range 23–89). Among tumors of endometrioid histology, 12 (48%) with serosal-only and 17 (19%) with adnexal-only involvement were FIGO grade 3 (p=0.007). Twenty-three tumors with serosal-only (64%) and 50 with adnexal-only (37%) involvement had lymphovascular invasion (p=0.004). Non-endometrioid histology was present in five tumors (83%) with combined adnexal/serosal, 15 (38%) with serosal-only, and 50 (36%) with adnexal-only involvement.

Median follow-up was 77 months (range 0.6–254). Five-year progression-free survival and overall survival rates for all patients with stage IIIA disease were 73.8% (SE 3.5%) and 81.0% (SE 3.1%), respectively. For patients with adnexal-only, serosal-only, and combined adnexal/serosal involvement, 5-year progression-free survival rates were 80% (SE 3.8%), 61% (SE 8.3%), and 33% (SE 19.2%), respectively (p<0.01); 5-year overall survival rates were 85% (SE 3.3%), 70% (SE 7.8%), and 60% (SE 21.9%), respectively (p=0.09). On univariate analysis, tumors having serosal involvement with/without adnexal involvement, non-endometrioid histology, and lymphovascular invasion were significantly associated with progression. On multivariate analysis, tumors having serosal involvement with/without adnexal involvement remained significantly associated with recurrence (adjusted HR=2.2, 95% CI 1.2 to 4.3; p=0.01).

Conclusions Patients with 2009 FIGO stage IIIA endometrial cancer have distinct survival outcomes depending upon adnexal and/or serosal involvement. Progression-free survival was worse for patients with serosal involvement after adjusting for histology, adjuvant treatment, and lymphovascular space invasion.