Can reduced field-of-view diffusion sequence help assess microsatellite instability in FIGO stage 1 endometrial cancer?

Purpose: To determine if a reduced-field-of-view (rFOV) diffusion intravoxel incoherent motion (IVIM) sequence can differentiate the imaging characteristics of tumors with microsatellite instability (MSI) from those that are microsatellite stable (MSS) in patients with clinical FIGO stage IA endometrial cancer and if MRI can be used to determine MSI status. Materials and Methods: Sagittal rFOV diffusion-weighted images were obtained in 12 patients on a 3T scanner using six b-values (0, 50, 100, 150, 200, and 600). These images were used to derive apparent diffusion coefficient (ADC), true diffusion coefficient (D_t), pseudodiffusion (D*), and perfusion fraction (f). Regions of interest (ROIs) were drawn on the dynamic contrast-enhanced magnetic resonance imaging (MRI) sequence on an Advantage Windows workstation and were copied to the same location on IVIM-derived images. The ROI mean of these images was recorded and compared with the microsatellite status. The depth of myometrial invasion and IVIM-derived parameters were tabulated by microsatellite status. The Wilcoxon rank sum test was used to compare T₁ postcontrast images and IVIM-derived images and microsatellite status. Results: Six patients had MSS tumors and six had MSI tumors. MSS tumors had a significantly higher ADC value (P = 0.03) and D_t (P = 0.045) than the MSI tumors. There was no association between < and ≥ 50% depth of myometrial invasion (measured on pathology and MRI analysis) and MSI stability P > 0.99. Conclusion: IVIM, ADC and D_t may be able to determine microsatellite status noninvasively in patients with clinical FIGO stage I endometrial cancer. Level of Evidence: 1. J. Magn. Reson. Imaging 2017;45:1216–1224.