Is the standard deviation of the apparent diffusion coefficient a potential tool for the preoperative prediction of tumor grade in endometrial cancer?

Background: The tumor histological grade is closely related to the prognosis of endometrial cancer (EC). The use of the apparent diffusion coefficient (ADC), tumor volume, and MRI-based texture analysis has allowed exciting advances in predicting EC grade before surgery. However, whether this constitutes a simple, convenient, and powerful diagnostic method remains unknown. Purpose: To explore the utility of standard deviation (SD) of the ADC (ADC_SD) for predicting the tumor grade in patients with EC. Material and Methods: We retrospectively evaluated 138 patients with EC. All patients underwent unenhanced MRI and diffusion-weighted imaging (DWI). The mean ADC value (ADC_mean) and SD were obtained using a freehand region of interest traced on the ADC map. Spearman’s linear correlation coefficients were calculated to analyze the correlations between the indexes (including ADC_SD and the ADC_mean) and the Ki-67 index. The Kruskal–Wallis and Mann–Whitney U tests were used to compare differences in the index results among tumor grades. Results: A significant difference in ADC_SD was observed among the tumor grades (P=0.000), and the ADC_SD value was significantly higher for high-grade EC than for low-grade tumors (289.7 vs. 216.3×10⁻⁶mm² /s, P=0.000). A statistically significant positive correlation was observed between ADC_SD and the Ki-67 index (r=0.364, P=0.000). According to the receiver operating characteristic curve, ADC_SD ≥240.2×10⁻⁶mm² /s predicted high-grade EC with a sensitivity, specificity, and accuracy of 73.1%, 80.2%, and 77.5%, respectively. Conclusion: Based on the intratumor heterogeneity of EC, ADC_SD represents a potential method for the preoperative prediction of high-grade EC, although further studies are needed.