MP50-08 DIFFUSION-WEIGHTED MRI AS AN IMAGING BIOMARKER OF THE FUHRMAN NUCLEAR GRADE OF CLEAR CELL RENAL CELL CARCINOMA

INTRODUCTION AND OBJECTIVE: Diffusion-weighted MRI (DWI) is a functional imaging method that visualizes the degree of water molecule diffusion within tissues. Its quantitative index, the apparent diffusion coefficient (ADC), is expected to be an imaging biomarker that reflects the histological characteristics of a tumor. Conventionally, ADC values are obtained from a representative slice of a tumor but this does not fully reflect all of the tumor features, especially in tumors with intra-tumor heterogeneity, such as renal tumors. To utilize the ADC as an imaging biomarker for tumors, an objective method for the volumetric analysis of the whole tumor part or solid tumor part would be ideal. We recently developed a new imaging software BDscore (PixSpace, Ltd., Japan) for volumetric ADC analysis. We investigated the usefulness of volumetric ADC analysis as an imaging biomarker of the Fuhrman nuclear grade (FG) of clear cell renal cell carcinoma (ccRCC). METHODS: Of the patients who underwent DWI (b-values of 0 and 1000 sec/mm2) before partial or radical nephrectomy between 2014 and 2016, a total of 39 patients, all of whom were histologically diagnosed with ccRCC, pT1, were retrospectively analyzed. We analyzed the DWI using BDscore. Those pixels of the whole tumor part and the solid tumor part with an ADC value from 0.3 to 1.5 × 10-3 mm2/s were identified in all of the image slices, and ADC histograms of the whole tumor part (WT-ADC) and the solid tumor part (ST-ADC) were created. We compared the ADC analysis parameters, including the mean value, kurtosis and skewness, with the FG. RESULTS: The FG was 1/2 in 25 (56%) and 3/4 in 14 (44%). The median diameters of FG 1/2 and FG 3/4 tumors were 4.0 mm (range, 3.0–5.8 mm) and 5.4 mm (4.1–7.3 mm), respectively (p=0.0002). All of the tumors showed a high signal intensity on DWI (b-value: 1000 s/mm2). The DWI signals were heterogenous and homogeneous in 32 (82%) and 7 (18%) patients, respectively. The mean WT-ADC value of FG 3/4 was significantly lower than that of FG 1/2 (1.58×10-3 vs. 1.91×10-3 mm2/s, p=0.029). There were no significant differences among the other WT-ADC-related parameters, nor the mean ST-ADC-related parameters. CONCLUSIONS: The mean WT-ADC reflects the FG of ccRCC. Therefore, the volumetric analysis of a DWI can be a potential imaging biomarker for predicting the aggressiveness of ccRCC.Source of Funding: None