There are several types of malignant tumors under this category; the most common one being adenocarcinoma.
Adenocarcinoma
Although most colorectal adenomas (polyps) do not develop into adenocarcinomas -- most adenocarcinomas develop from adenomas -- therefore, they are considered as precursor lesions.
Morphology
- Can appear anywhere in the colon
- In the right colon -- appear as polypoid, exophytic masses, rarely causing obstruction
- In the left colon -- appear as annular lesions resembling a "napkin ring" causing luminal obstruction
- Regardless of their growth pattern, adenocarcinomas show ulcerations
Pathogenesis
As with other types of cancer, the cause is genetic and epigenetic alterations.
The two main genetic pathways that are responsible for the development and progression of colorectal adenocarcinoma are:
- APC/β-catenin pathway
- Responsible for the majority of colorectal