ملف:Adenocarcinoma of the Sigmoid Colon (longitudinal section, closeup).jpg

Adenocarcinoma of the Sigmoid Colon (longitudinal section, closeup)

The closeup of the longitudinal section shows that the tumor, despite its unimpressive size, demonstrates evidence of superficial invastion of the muscularis propria.

Microscopically, the deep aspect of the tumor consisted of a mucinous component. Free-floating tumor cells were present in mucin lakes in the deep muscularis propria, and one of the acellular mucin lakes actually penetrated completely through the muscle along a neurovascular bundle. For staging, I was faced with deciding whether the presence of mucin alone constituted full-thickness invasion (T2 versus T3), Ultimately I was impressed with the aggressive behavior of such a small tumor, so I opted to stage it as T3.