Robotic sentinel lymph node (SLN) mapping in endometrial cancer: SLN symmetry and implications of mapping failure

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.