Sentinel lymph nodes (SLN) in endometrial cancer: The relationship between primary tumor histology, SLN metastasis size, and non-sentinel node metastasis.

Objectives: To examine sentinel lymph node pathology and describe relationships to uterine pathology, non-sentinel pelvic lymph nodes, and para-aortic lymph nodes.

Methods: Patients with apparent uterine-confined endometrial cancer underwent robotic hysterectomy, SLN mapping, completion pelvic lymphadenectomy (LND), and para-aortic (PaLND) directed by frozen section. Patients were risk stratified by histology: low-risk (LR) endometrioid <50% depth-of-invasion (DOI), intermediate-risk (IR) endometrioid ≥50% DOI, and high-risk (HR) type II histology for comparison to other pelvic/aortic metastases.

Results: 414 patients were stratified: 275 LR, 80 IR, and 59 HR cases. PaLND was performed in 84.2% of IR/HR patients and 25.1% LR patients. Pelvic node metastasis was detected in 11.6% LR, 50.0% IR, and 39.0% HR patients. PaLN metastasis was detected in 2.9% LR, 11.3% IR, and 16.9% HR patients. Proportionally, isolated tumor cells (ITC) SLNs were more common in LR or IR vs. HR group (51.6% and 44.7% vs. 15.0%, p < 0.05). The SLN false negative rates (FNR) were 0% LR, 2.5% IR, and 5.1% HR. Non-sentinel pelvic node metastases were present in 28(31.5%) of all SLN+ cases, but only 3(8.3%) of SLN with ITC. PaLN metastasis was found in 18.8% LR, 11.8% IR, and 33.3% HR cases with ITC SLNs. After controlling for DOI, LVSI, and grade, ITC-positive SLNs had a significant association with non-sentinel pelvic and aortic metastasis (p = 0.03 and p = 0.008, respectively).

Conclusions: Patients with HR histology have more micro/macro-metastases in both SLNs and non-SLN metastases compared to LR/IR patients. SLN ITCs were associated with a clinically significant incidence of PaLN metastasis across all histology risk groups. There were no cases of isolated aortic node metastasis in this study. SLN mapping had an increased, although clinically acceptable FNR in the HR cohort compared to LR patients.