Introduction Several studies have reported optimizing ultrastaging protocols using immunohistochemistry for sentinel lymph node (SLN) biopsy in endometrial carcinoma; however, the clinical significance of isolated tumor cells (ITCs) detected by ultrastaging is unknown. This study aimed to: (1) determine the frequency of retrospective ITC detection in patients with endometrial carcinoma and reported negative SLNs determined by hematoxylin and eosin (H&E) examination only; and (2) determine the clinicopathological features and outcomes of patients with endometrial carcinoma and previously undetected ITCs.

Methods 474 SLNs from 155 patients with endometrial carcinoma and reported negative SLNs were subjected to an immunohistochemistry protocol which included staining slides with cytokeratin at 1, 10, 20, and 50 µm levels, to examine for ITCs. Clinicopathological data of patients with ITCs detected by this method were analyzed to determine patient outcomes.

Results Using immunohistochemistry, ITCs were detected in 5.7% (27/474) of SLNs and 13.5% (21/155) of patients with previously reported negative SLNs. In this patient cohort, 95.2% (20/21) had endometrioid histology, with the remaining case being carcinosarcoma. 38.1% (8/21) received adjuvant therapy (either brachytherapy alone (4/8) or chemotherapy and radiation (4/8)) based on other parameters, while 61.9% (13/21) had no adjuvant therapy. Of the patients who did not receive adjuvant therapy, all had endometrioid histology and 84.6% (11/13) were International Federation of Gynecology and Obstetrics (FIGO) stage IA. No patients (0/13) recurred after a median follow-up of 31.5 (range 2–84.4) months.

Discussion In this study, 38.1% of patients with previously undetected ITCs had adjuvant treatment based on other high risk factors; as such, reporting ITCs would not have altered patient management for those who received adjuvant chemotherapy. To date, no patients with previously undetected ITCs without adjuvant treatment had a recurrence, suggesting that ITC detection may not be clinically relevant.