What is Colorectal Cancer?

What is Colorectal Cancer?


The colon and rectum

Colon and rectum are parts of our digestive system. They are together known as large bowel.

The colon absorbs large quantities of water, salts, and nutrients from undigested remaining food material as they pass through it.

The waste material that remains after being absorbed in the colon goes to the rectum. The rectum is located at the end of the colon and stores feces and waste material before they are passed out of the body through the anus. Rectum is the last 6 inches chamber of the digestive system.

Overview of Colorectal Cancer

Colorectal cancer, also known as bowel cancer, colon cancer or rectal cancer, depending on where they start from, is a cancer of the colon and the rectum. It starts in the colon or the rectum. Colon cancer and rectal cancer are often grouped together because many features are common in them.

According to World Health Organization and CDC, it is the second most common cancer worldwide, after lung cancer. According to American Cancer Society, about 1 in 20 people in the US will develop colorectal cancer during their lifetime.

The risk of developing colorectal cancer is slightly higher in men than in women. Most people diagnosed with it are above the age of 60.

How Does Colorectal Cancer Start?

Mostly, colorectal cancers start as a growth called a polyp on the inner lining of the colon or the rectum. Not all polyps are cancerous, but some polyps can change into cancer over a period of several years. There are two main types of polyps:

  • Adenomatous polyps (adenomas): These polyps can convert into cancers. They are also called pre-cancerous conditions.
  • Hyperplastic polyps and inflammatory polyps: These polyps are often not pre-cancerous. These are more common than adenomatous polyps.

A polyp can grow into the wall of the colon or rectum if a cancer is formed in it. Finding and removing the polyps can help prevent the colorectal cancer.

Polyps may be small and may show no or little symptoms. Therefore, doctors recommend regular screening tests to help diagnose them and prevent their spread before they become colon cancer. To know about signs and symptoms of colorectal cancer read here.

The size of these polyps is linked to the development of cancer. Polyps less than 1 centimetre in size have a slightly lesser chance of becoming cancer, but those polyps that are larger than 2 centimetres have significantly higher chance of converting into cancer. Mostly, the colorectal cancers form from polyps in glandular tissues of intestinal linings.

The wall of the colon and rectum is made up of several layers. Colorectal cancer begins in the innermost layer, called mucosa, and can grow outward through other layers. Cancer cells can also grow into blood vessels or lymph vessels from where they can travel to surrounding lymph nodes or to various organs of the body. Based on how deep and far the cancer grows indicates the stage of the colorectal cancer.
If the colorectal cancer is diagnosed early and treated properly, when the tumor is still localized, there are greater chances of getting the cure – with about 5 year survival rates of about 90%. However, if the tumor continues to grow, the colorectal cancer can spread through the bowel wall to nearby lymph nodes, tissues, and organs, and into the bloodstream. In such conditions, successful treatment is difficult. You can know about tests and diagnosis of colorectal cancer here.