Lymph Node Isolated Tumor Cells in Patients With Endometrial Cancer.

Importance: Isolated tumor cells (ITCs) are the histopathological finding of small clusters of cancer cells no greater than 0.2 mm in diameter in the regional lymph nodes. For endometrial cancer, the prognostic significance of ITCs is uncertain. Objective: To assess clinico-pathological characteristics and oncologic outcomes associated with ITCs in endometrial cancer. Design, Setting, and Participants: This retrospective cohort study using the National Cancer Database included patients with endometrial cancer who had primary hysterectomy and nodal evaluation from 2018 to 2020. Patients with microscopic and macroscopic nodal metastases and distant metastases were excluded. Data were analyzed from June to September 2023. Exposure: Regional nodal status with ITCs (N0[i+] classification) or no nodal metastasis (N0 classification). Main Outcomes and Measures: (1) Clinical and tumor characteristics associated with ITCs, assessed with multivariable binary logistic regression model, and (2) overall survival (OS) associated with ITCs, evaluated by nonproportional hazard analysis with restricted mean survival time at 36 months. Results: A total of 56 527 patients were included, with a median (IQR) age of 64 (57-70) years. The majority had T1a lesion (37 836 [66.9%]) and grade 1 or 2 endometrioid tumors (40 589 [71.8%]). ITCs were seen in 1462 cases (2.6%). In a multivariable analysis, ITCs were associated with higher T classification, larger tumor size, lymphovascular space invasion (LVSI), and malignant peritoneal cytology. Of those tumor factors, LVSI had the largest association with ITCs (7.9% vs 1.4%; adjusted odds ratio [aOR], 4.37; 95% CI, 3.87-4.93), followed by T1b classification (5.3% vs 1.3%; aOR, 2.62; 95% CI, 2.30-2.99). At the cohort level, 24-month OS rates were 94.3% (95% CI, 92.4%-95.7%) for the ITC group and 96.1% (95% CI, 95.9%-96.3%) for the node-negative group, and the between-group difference in expected mean OS time at 36 months was 0.35 (SE, 0.19) months, but it was not statistically significant (P = .06). There was a statistically significant difference in OS when the low-risk group (stage IA, grade 1-2 endometrioid tumors with no LVSI) was assessed per nodal status and adjuvant therapy use (P < .001): (1) among the cases treated with surgical therapy alone, 24-month OS rates were 95.9% (95% CI, 89.5%-98.5%) for the ITC group and 98.8% (95% CI, 98.6%-99.0%) for the node-negative group, and the between-group mean OS time difference at 36 months was 0.61 (SE, 0.43) months (P = .16); and (2) among the cases with ITCs, adjuvant therapy (radiotherapy alone, systemic chemotherapy alone, or both) was associated with improved survival compared with no adjuvant therapy (24-month OS rates, 100% vs 95.9%; between-group mean OS time difference at 36 months, 0.95 [SE, 0.43] months; P = .03). Conclusions and Relevance: In this cohort study of patients with surgically staged endometrial cancer, the results of exploratory analysis suggested that presence of ITCs in the regional lymph node may be associated with OS in the low-risk group. While adjuvant therapy was associated with improved OS in the low-risk group with ITCs, careful interpretation is necessary given the favorable outcomes regardless of adjuvant therapy use. This hypothesis-generating observation in patients with low-risk endometrial cancer warrants further investigation, especially with prospective setting.