What is Colorectal cancer?

Colon cancer starts in the colon or rectum. These cancers may moreover be called colon cancer or rectal cancer, depending on where they begin. Colon cancer and rectal cancer are often grouped because they share many characteristics.

                                Colon and rectum

The colon and rectum make up the large intestine (or colon), which is part of the digestive system, also known as the gastrointestinal (GI) system. Most of the colon is made up of the large intestine, a muscular tube about 5 feet (1.5 meters) long. The parts of the large intestine are named after the food traveling through them. The first part is called the ascending colon. It begins in a pouch called the cecum, where undigested food comes from the small intestine. It continues upwards on the right side of the stomach (abdomen).

The other part is called the transverse colon. It goes from right to left throughout the body. The third part is called the descending colon because it descends (travels down) on the left side. The fourth segment is called the sigmoid colon because of its “S” shape. The sigmoid colon connects to the rectum, which then connects to the anus.

The ascending and transverse parts together are called the proximal colon. The descending and sigmoid colon is called the distal colon.

                     Function of colon and rectum work

The large intestine absorbs water and salt from the rest of the food after it passes through the small intestine (small intestine). After passing through the large intestine, the waste that remains is the last 6 inches (15 cm) of the digestive system into the rectum. It stays there until it passes through the anus. Ring-shaped muscles around the anus (also called sphincters) prevent stool from coming out until they relax during a bowel movement.

                           Starting of colorectal cancer

Polyps in the colon or rectum:

Most colorectal cancers start as developments on the inward lining of the colon or rectum. These developments are called polyps. Some sorts of polyps can turn into cancer over time (more often than not a few a long time), but not all polyps end up cancerous.

The likelihood that a polyp will turn into cancer depends on what type it is. There are different types of polyps.

Adenomatous polyps (adenomas): These polyps sometimes turn into cancer. Because of this, adenomas are called precancerous conditions. The 3 types of adenomas are tubular, villous, and tubular.

Hyperplastic Polyps and Inflammatory Polyps: These polyps are more common, but are not usually preceded by cancer. Some people with large (greater than 1 cm) hyperplastic polyps may need colon cancer screening with a colonoscopy.

Sessile serrated polyps (SSP) and conventional serrated adenomas (TSA): These polyps are often treated like adenomas because they carry a higher risk of colorectal cancer.

Other factors that can make a polyp more likely to become cancerous or increase one’s risk of colorectal cancer include:

  • If a polyp larger than 1 cm is found.
  • If more than 3 polyps are found.
  • If dysplasia is seen after the polyp is removed. Dysplasia is another precancerous condition. This means that there is an area in the polyp or in the lining of the colon or rectum where the cells look abnormal, but have not become cancerous.

                           Progression of colorectal cancer

If cancer forms in a polyp, it can eventually grow into the wall of the colon or rectum. The divider of the colon and rectum is made up of a few layers. Colorectal cancer starts in the innermost layer (mucosa) and may spread outward through some or all of the other layers.

When cancer cells are in the wall, they can grow into blood vessels or lymph vessels (small channels that carry waste and fluid). From there, they can travel to nearby lymph nodes or distant parts of the body.

The stage (extent of spread) of colon cancer depends on how deep it has grown into the wall and if it has spread outside the colon or rectum.

Types of colon and rectal cancer:

Most colorectal cancers are adenocarcinomas. These cancers begin in the cells that make mucus to lubricate the inside of the colon and rectum. When specialists conversation about colorectal cancer, they’re nearly continuously talking approximately this sort.

Certain subtypes of adenocarcinoma, such as signet ring and mucinous, may have a worse prognosis (outlook) than other subtypes of adenocarcinoma.

Other, less common types of tumors can also start in the colon and rectum. These include:

  • Carcinoid tumor. They begin with specialized hormone-producing cells in the intestine. See Carcinoid tumor of the stomach.
  • Gastrointestinal stromal tumors (GISTs) originate from specialized cells of the colon wall called interstitial cells of Cajal. Some are benign (not cancerous). These tumors can occur anywhere in the digestive tract but are not common in the colon.
  • Lymphomas are cancers of cells of the immune system. They most often start in the lymph nodes, but they can also start in the colon, rectum, or other organs. Information about lymphoma of the digestive system can be found at Non-Hodgkin Lymphoma.
  • Sarcomas can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare.