Introduction/Background More than half of all endometrial cancers are diagnosed as early stage low-risk, and are treated with surgery alone. However, 3–10% of them experience relapse. The aim of this study is to evaluate risk factors and patterns of recurrence in patients with low-risk endometrial cancer.

Methodology Patients who diagnosed with endometrial cancer after hysterectomy at Seoul St. Mary’s hospital and St. Vincent hospital from 2009 to 2019 were identified. The inclusion criteria are as follows: FIGO stage Ia; endometrioid adenocarcinoma grade 1–2; and no lymphovascular space invasion. Exclusion criteria are those who received postoperative adjuvant treatment. Survival was analyzed using Kaplan-Meier method, and significance was confirmed using the log-rank test. Multivariate analysis was performed using the Cox proportional hazards regression method.

Results A total of 391 patients were included and the median follow-up period was 53 months. Of those, 22 (5.6%) had recurrence, and 5 (1.3%) died of disease. Multivariate analysis identified menopause and tumor grade 2 as independent risk factors for recurrence. Of note, 10 of 62 patients (16.1%) with both risk factors relapsed, suggesting that postoperative adjuvant therapy could be considered for these patients. The most common sites of recurrence are vaginal stump and lung (7/22, 31.8%). In vaginal stump recurrence, the median time to recurrence was shorter than that of other sites (30 vs 15 months, p = 0.002), and 71.4% (5/7) were isolated recurrence. Median time to recurrence was 31 and 25 months for G1 and G2, respectively (p = 0.130).

Conclusion We identified menopause and tumor grade 2 as risk factors for recurrence in early stage low-risk endometrial cancer. Since lung is one of the most common sites of recurrence and usually does not develop symptoms, routine check during follow-up is required.