To establish the bilateral pelvic concordance rate of the sentinel lymph node (SLN) and determine the likelihood of lymph node metastasis in cases of mapping failure.

A database analysis was performed on 414 patients with clinical stage I endometrial cancer who underwent SLN mapping followed by robotic hysterectomy and completion pelvic (n=414, 100%) and aortic (n=186, 44.9%) lymphadenectomy from March 2011 to August 2016. Stage, histology, SLN sites, and surgico-pathologic findings were analyzed. The bilateral concordance rate of SLN location, successful unilateral and bilateral mapping rates, false negative rate, and non-SLN metastasis associated with mapping failure were calculated.

Histologies included 354 (85.5%) endometrioid, 39 (9.4%) serous, 16 (3.9%) carcinosarcoma, 4 (1.0%) clear cell, and 1 (0.2%) undifferentiated. Final stages included 262 (63.3%) IA, 36 (8.7%) IB, 15 (3.6%) II, 6 (1.4%) IIIA, 68 (16.4%) IIIC1, and 27 (6.5%) IIIC2. Bilateral SLN mapping was successful in 355 (85.7%) patients, and 266 (74.9%) demonstrated mapping to the symmetrical lymphatic group contralaterally. The mapping failure rate was 13.5% (56/414) unilaterally and 0.7% (3/414) bilaterally. SLN locations were external iliac (69.1%), obturator (25.1%), internal iliac (2.2%), common iliac (1.9%), pre-sacral (0.9%), aortic (0.4%), parametrial (0.3%), and para-rectal (0.1%). Lymph node metastases were identified in 95 (22.9%) pelvic and 27 (6.5%) aortic nodes. 10 (16.9%) cases with mapping failure had lymph node metastasis on completion lymphadenectomy, similar to the proportion of SLNs with metastases (p=0.35). However, macro-metastases were more common in mapping failure completion lymphadenectomies than in the positive SLNs (80% vs 22.3%, p<0.001).

The contralateral SLN location concordance rate was 75%. Most SLNs were along the medial external iliac or obturator locations. The rate of positive lymph nodes associated with SLN mapping failure was 16.9%, similar to the overall node-positive rate. The detection of pelvic node metastasis with SLN mapping failure was largely populated with macro-metastases and confirms the necessity of completion lymphadenectomy with mapping failure.