Objective Missing occult para-aortic lymph node metastasis is one of the primary concerns of sentinel lymph node biopsy in endometrial cancer. Our study aimed to evaluate the relationship between intrauterine cancer site and isolated para-aortic lymph node metastasis to tailor treatment and reduce the false negative rate of the sentinel lymph node procedure.

Methods A retrospective, multicenter, case control study was performed in four international centers. All patients with positive lymph nodes who had complete surgical staging with pelvic and para-aortic lymphadenectomy, between January 2013 and December 2023, were included. Detailed descriptions of the cancer location within the uterine cavity on the cranio-caudal plane and the myometrial wall involvement on the cranio-caudal and ventro-dorsal planes were collected, as were clinical data and cancer histological features. Patients with isolated para-aortic lymph node metastasis were allocated to group 1; patients with pelvic lymph node metastasis and those with both pelvic and para-aortic lymph node metastasis were allocated to group 2. The groups were compared according to the variables collected.

Results 200 preoperative early stage endometrial cancer patients with postoperative International Federation of Gynecology and Obstetrics 2009/2023 stage IIIC1/IIIC2 were included in our study: 42 patients (21%) with isolated para-aortic lymph node metastasis were allocated to group 1 and the remaining patients to group 2. The two groups had comparable clinical and pathological characteristics (p>0.05): mean age was 66.5±10.3 (group 1) and 63.5±11.9 (group 2); endometrioid histotype was the predominant one for both groups (50%); most patients had myometrial infiltration >50% (80.9% and 79.7%), grade 3 (61.9% and 63.9%), and lymph vascular space invasion (78.5% and 82.2%). Cancers involving the fundal uterine cavity, the fundal myometrial wall, or the anterior myometrial wall were 3.11 (1.04–9.27), 3.03 (1.12–8.21), and 2.12 (0.77–5.80) times more likely to metastasize only to para-aortic lymph nodes compared with cancers located in other uterine sites.

Conclusions In this study, the intrauterine location of the cancer determined the site of lymph node metastasis. When the tumor involved the fundus (cavity or wall) and infiltrated exclusively the anterior wall, the baseline risk of spreading only into the para-aortic area increased significantly in selected patients at risk of nodal disease.