Definition
Colorectal cancer is either generated from the colon or rectum. Depending upon the origin of cancer development it can term as colon cancer or rectal cancer. Both colon and rectal cancers are grouped as they have some similar features.
Anatomy and physiology of colon and rectum
Anatomically, the colon is a muscular long tube of the large intestine with almost 5 feet length, which is divided into four major parts ascending colon (first part), transverse colon (second part), descending colon (third part), and sigmoid colon (fourth part). Whereas, rectum with 15 cm length is a passage between the colon and anus. These organs are associated with the gastrointestinal system.
The colon absorbs water and salt from the remaining food material after finishing the absorption process in the small intestine. The waste matter remains in the colon then passes to the rectum and stores until it passes through the anus.
How Colorectal cancer develops?
Inner lining growth which is also known as polyps formation may be the start of colorectal cancer. However, all the polyps are not cancerous. Depending upon the type of polyp it turns to cancer. Following are different types of polyps:
Adenomatous polyps or adenomas polyps: These are considered a pre-cancerous condition, as this type of polyp may turn to cancer. Tubular, villous, and tubulovillous are three different classifications of adenomas.
Hyperplastic polyps and inflammatory polyps: These are common types of polyps, but generally they are not pre-cancerous. But larger sized polyps with more than 1 cm need to screen for colorectal cancer. A colonoscopy test is conducted in a clinical laboratory for screening purposes.
Sessile serrated polyps (SSP) and traditional serrated adenomas (TSA): These are also considered as adenomas type of polyps as the development of such polyps increases the risk of colorectal cancer.
Certain factors also responsible for considering any polyp development turns to colorectal cancer, which is as follows:
- Large size polyps that are more than 1 cm
- Development of three or more polyps
- Abnormal cells or dysplasia present in the lining of the colon or rectum after removal of the polyp is also considered as a pre-cancerous condition. Dysplasia can turn into cancer.
Colorectal cancer spreading
Cancerous polyp can grow multilayered walls of the colon and rectum. Colorectal cancer can grow inner or outermost layers and gradually spread to outer or inner layers. Colorectal cancer develops in the wall and can spread to the adjoining blood vessels or lymph vessels. From there, it travels to the lymph node and other distant organs.
Types of colorectal cancer?
Colorectal cancers are usually adenocarcinomas. This type of colorectal cancer is mainly developed at mucus-producing cells which makes the colon and rectum lubricated. Adenocarcinomas have subtypes like signet ring and mucinous and provide worsen prognosis.
Apart from this, less commonly developed tumors in the colon and rectum are carcinoid tumors, gastrointestinal stromal tumors, lymphomas, and sarcomas.
Reference
https://www.cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html
