Colorectal cancer is a cancer that starts in the colon or the rectum. This cancer can also be named colon cancer or rectal cancer, depending on the part of the intestine where the cancer begins. Colon cancer and rectal cancer are often grouped due to their common and similar features. This cancer may be benign, or non-cancerous, or malignant. Being a malignant cancer, it means it can spread to other parts of the body and damage them.

Colon cancer typically affects older adults, though it can happen at any age. It usually begins as small, noncancerous (benign) clumps of cells called polyps that form on the inside of the colon. Over time some of these polyps can become colon cancers.

Polyps may be small and produce few, if any, symptoms. For this reason, doctors recommend regular screening tests to help prevent colon cancer by identifying and removing polyps before they turn into cancer.

If colon cancer develops, many treatments are available to help control it, including surgery, radiation therapy and drug treatments, such as chemotherapy, targeted therapy and immunotherapy.

Colorectal cancer is much more common among black men than people of other races. In the United States of America, it is estimated that 1 in 22 men and 1 in 24 women would develop colorectal cancer in their lifetime.

The Colon and Rectum

The colon is the longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum (which is the final six inches of the large intestine closest to the anus) and leaves the body through the anus.

Colorectal Cancer in Nigeria

Colon cancer, which affects men and women, is one of the most common cancers globally. About 45 years ago, colorectal cancer (CRC) in Nigeria used to be a rare disease but recently it has gradually become a highly significant health issue in the country. Several medical writers and teaching hospital had researched on what could have brought about the high significance of this form of cancer, yet none could highlight the main reason.

Colorectal cancer is the third most common cancer among Nigeria men after prostate and liver cancer, and the fourth most common cancer in Nigeria women after breast, cervical and liver cancer.

In the year 2016, it was recorded that approximately 49,190 people died from colorectal cancer; and yet over 55,000 confirmed deaths have been recorded till date.

How Colorectal Cancer Start

Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps.

Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp changing into cancer depends on the type of polyp it is. The 2 main types of polyps are:

• Adenomatous Polyps (Adenomas):These type of polyps sometimes change into cancer and because of this, adenomas are usually called a pre-cancerous condition.
• Hyperplastic Polyps and Inflammatory Polyps:These polyps are more common, but in general they are not pre-cancerous.

Other factors that can make a polyp more likely to contain cancer or increase someone’s risk of developing colorectal cancer include:

• If a polyp larger than 1 cm is found
• If more than 2 polyps are found
• If dysplasia is seen in the polyp after it's removed. Dysplasia is another pre-cancerous condition. It means there's an area in a polyp or in the lining of the colon or rectum where the cells look abnormal, but they don't look like true cancer cells.

Types of Colorectal Cancer

Adenocarcinomas: This make up about 96% of colorectal cancers. These cancers start in cells that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, they're almost always talking about this type. Some sub-types of adenocarcinoma, such as signet ring and mucinous, may have a worse prognosis (outlook). 

There are other much less common types of tumors which can start in the colon and rectum, too. These include:

Carcinoid Tumors: These start from special hormone-making cells in the intestine.

Gastrointestinal Stromal Tumors (GISTs): This start from special cells in the wall of the colon called the interstitial cells of Cajal. Some are not cancer (benign). These tumors can be found anywhere in the digestive tract, but are not common in the colon.

Lymphomas: These are cancers of immune system cells. They mostly start in lymph nodes, but they can also start in the colon, rectum, or other organs. Information on lymphomas of the digestive system can be found in Non-Hodgkin Lymphoma.

Sarcomas: This type of colorectal cancer can start in blood vessels, muscle layers, or other connective tissues in the wall of the colon and rectum. Yet, sarcomas of the colon or rectum are quite rare.

[Next Week on Colorectal Cancer: How Colorectal Cancer Presents]