A 39-year-old woman with mid transverse colon cancer. Axial CT scan reveals irregular wall thickening with luminal narrowing of the transverse colon with pericolic fat infiltration (arrow). The visceral peritoneum was not identifiable and no solid organ invasion was visible, which suggested stage T3. However, the pathologic stage of this lesion proved to be pT4 because of tumor invasion into the visceral peritoneum.