Fig. 3. Discordant case between mrTRG and pTRG in 48-year-old man with rectal cancer.

A. On T2W axial image before CRT, tumor (arrows) showing intermediate high SI is located between 1 and 4 o'clock on rectum. B. After CRT, most of tumor was replaced by dark fibrosis. However, there is remaining lesion (arrows) with intermediate high signal. Radiologists reported as mrTRG 3 (> 50% fibrosis or mucin with intermediate tumor signal representing residual tumor, fibrosis > tumor). C. However, on microscopic pathologic slides (H&E stain; original magnification, × 12.5), most tumor cells are replaced by fibrosis (^*) and only scanty tumor cells (arrow) remain. Therefore, pathologists graded pTRG as 2. This is case in which TRG was overestimated by MR compared to pathology due to CRT-related inflammation and edema. TRG = tumor regression grade