Tumor Volume Index as a Predictor of Pelvic Lymph Node Metastasis in Low-Risk Endometrial Cancer

This study aimed to identify predictors of pelvic lymph node metastasis in low-risk endometrial cancer, defined as cases with no more than half myometrial invasion, preoperative endometrial biopsy results indicating endometrioid carcinoma Grade 1 (G1) or Grade 2 (G2), and no extrauterine spread. Among the factors examined, we focused on the tumor volume index derived from MRI, calculated by multiplying the maximum longitudinal diameter along the uterine axis, the maximum anteroposterior diameter on the sagittal plane, and the maximum transverse diameter on the horizontal plane. A retrospective analysis was conducted on 117 patients who underwent the standard treatment protocol (total hysterectomy, bilateral salpingo-oophorectomy, and pelvic lymph node dissection) at our institution from July 1, 2014, to December 31, 2023. Pelvic lymph node metastasis was observed in seven cases (5.9%). Univariate analysis showed a significant association with serum cancer antigen-125 (CA-125) level (p=0.035) and tumor volume index (p=0.003). A receiver operating characteristic (ROC) analysis revealed that a tumor volume index cutoff of 38 cm³ yielded an area under the curve (AUC) of 0.83, with a true positive fraction (TPF) of 0.86 and a false positive fraction (FPF) of 0.15. Multivariate analysis also identified a tumor volume index (≥38 cm³) as an independent predictive factor (odds ratio 26.3, 95% confidence interval 2.6-272, p=0.006). Cases with a tumor volume index ≥38 cm³ accounted for 23 cases (20% of all) of the cohort; among these, six cases (25%) had pelvic lymph node metastases. In contrast, the metastasis rate was only one case (1%) in 94 cases (80% of all) with a tumor volume index <38 cm³. These findings suggest that the tumor volume index is useful for evaluating the risk of pelvic lymph node metastasis in low-risk endometrial cancer, contributing to decision-making on whether to perform pelvic lymph node dissection and risk stratification for sentinel lymph node navigation surgery.