Prognostic value of isolated tumor cells in sentinel lymph nodes in intermediate-risk endometrial cancer: results from an international, multi-institutional study

Objective: This study assessed oncologic outcomes of patients with intermediate-risk endometrioid endometrial cancer and isolated tumor cells (ITC) (≤0.2 mm or ≤200 cells) in sentinel lymph nodes (SLNs). Methods: Patients with SLN-ITC diagnosed between 2012 and 2019 were identified from 19 centers worldwide, while SLN-negative patients were identified at Mayo Clinic, Rochester between 2014 and 2018. Only patients with endometrioid endometrial cancer and intermediate-risk factors (low-grade endometrioid histology and myometrial invasion ≥50%; high-grade endometrioid histology and myometrial invasion <50%) were included. Oncologic outcomes were evaluated by grouping patients according to prognostic factors: SLN-ITC and lymphovascular space invasion (LVSI). SLN-ITC patients with post-operative observation or vaginal brachytherapy (VB) alone were compared with similar node-negative patients. Results: Of the 166 patients included, those with simultaneous presence of SLN-ITC and LVSI were at higher risk of non-vaginal recurrence (HR 3.73 [95% CI 1.17 to 11.84], p = .01) compared with patients who were node-negative with no LVSI. Among the 122 patients (28 SLN-ITC, 94 node-negative) who underwent post-operative observation or VB alone, 1 isolated vaginal recurrence was documented in a node-negative patient, while non-vaginal recurrence occurred in 3 of 28 (10.7%) SLN-ITC and 7 of 94 (7.4%) node-negative patients. The median follow-up was 2.4 years (interquartile range; 1.8-3.0) among the remaining 25 ITC patients and 2.8 years (interquartile range; 0.8-4.2) among the remaining 87 node-negative patients. There was no difference in non-vaginal recurrence–free survival (SLN-ITC: 87.3% [95% CI 74.7% to 100.0%] vs node-negative: 82.2% [95% CI 69.1% to 97.9%], p = .46) or overall survival (SLN-ITC: 76.4% [95% CI 54.3 to 100.0] vs node-negative: 84.5% [95% CI 75.0 to 95.2], p = .28) between the 2 cohorts. Conclusions: In patients with endometrioid endometrial cancer and intermediate-risk factors (including patients who received chemotherapy/external beam radiotherapy), the combination of SLN-ITC and LVSI was associated with worse prognosis compared with patients with no risk factors or only 1 risk factor. In the sub-group of patients who received post-operative observation or VB alone, SLN-ITC did not worsen prognosis relative to node-negative patients.