¹⁸F-FDG PET/MRI with high-resolution DWI characterizes the distinct phenotypes of endometrial cancer

Objectives: Endometrial cancers have been divided into estrogen-dependent type I and the less common clinically aggressive estrogen-independent type II. The aim of this study was to evaluate the capability of integrated FDG-PET/MRI to characterize the distinct phenotypes of endometrial cancer.

Methods: 30 patients with endometrial cancer (22 with type I including 17 G1 and 5 G2 endometrioid adenocarcinomas, and 8 with type II including 3 G3 endometrioid adenocarcinomas, 2 carcinosarcomas and 3 serous carcinomas) underwent pretreatment FDG-PET/MRI scan with simultaneous high-resolution, small field-of-view diffusion weighted imaging. SUV, apparent diffusion coefficient (ADC), and SUV-to-ADC ratio were compared between type I and II cancers and between low-risk (type I and stage IA) and high-risk (type II or stage IB ≤) cancers. The diagnostic accuracy for discriminating the cancer phenotypes was compared using receiver-operating-characteristic (ROC) analysis.

Results: Although SUV was not significantly different between type I and II endometrial cancers, type II cancer showed a significantly lower ADC (667±276 x 10^-6) and a greater SUV-to-ADC ratio (24.5±8.1 x 10⁹) than did type I cancer (924±145 x 10^-6, p=0.04, and 14.1±4.9 x 10⁹, p<0.001, respectively). High-risk endometrial cancer showed a significantly higher SUV (15.6±5.8), a lower ADC (758±242 x 10^-6), and a greater SUV-to-ADC ratio (21.7±7.5 x 10⁹) than did low-risk cancer (11.7±3.5, p=0.04, 941±153 x 10^-6, p=0.02, and 12.7±4.1 x 10⁹, p=0.001, respectively). In ROC analysis, the most accurate diagnostic index for predicting type I and II cancers and for predicting low-risk and high-risk cancers was SUV-to-ADC ratio. The optimal SUV-to-ADC cutoff value of 18.5 x 10⁹ for predicting type II cancer revealed 88% sensitivity, 86% specificity, and 87% accuracy, and the optimal cutoff of 13.6 x 10⁹ for predicting high-risk cancer revealed 86% sensitivity, 69% specificity, and 77% accuracy, that were significantly better than the 77% and 67% accuracy for SUV, respectively.

Conclusions: Endometrial cancer tends to increase tumor cellularity with accelerated glucose metabolism in higher histological grade or stage. The SUV-to-ADC ratio obtained by integrated FDG-PET/MRI reflects tumor aggressiveness and will be useful for noninvasive diagnosis and for deciding on the appropriate therapeutic strategy for patients with endometrial cancer.

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