- Objective To quantify the relative risk associated with lower uterine segment involvement (LUSI) on outcome measures in patients with apparent stage I endometroid endometrial cancer. Methods A cohort of 769 consecutive patients with endometroid endometrial carcinoma apparent stage I, who underwent surgery in five gynecological oncology centers in Israel; 138 patients with and 631 without LUSI were followed for a median time of 51 months. Local recurrence, recurrence-free and overall survival were compared between the two groups. Results LUSI was associated with grade 3 tumor ( p = 0.002), deep myometrial invasion ( p p = 0.01). There were 22 cases of local recurrences, 40 cases of distal recurrences and 80 patients died. Univariate survival analysis showed that patients with LUSI had trend toward lower regional recurrence-free survival ( p = 0.09), and significant lower distant recurrence-free survival ( p = 0.04) and lower overall survival ( p = 0.002). The Cox proportional hazards model demonstrated a significantly decreased overall survival (HR = 2.3; 95% CI 1.3, 3.9; p = 0.003) in cases with LUSI. Conclusions In patients with apparent stage I endometroid endometrial cancer, the presence of LUSI is a poor prognostic factor, associated with a significantly higher risk of distal recurrence and death. The presence of LUSI warrants consideration when deciding upon surgical staging or postoperative management.