What is colorectal cancer?

Colorectal cancer starts in the cells of the colon or rectum. A cancerous (malignant) tumour is a group of cancer cells that can grow into nearby tissue and destroy it. The tumour can also spread (metastasize) to other parts of the body.

The colon and rectum are parts of the large intestine and the digestive system. The colon absorbs water and nutrients and passes waste (stool or poop) to the rectum. Colon and rectal cancers are grouped together as colorectal cancer because these organs are made of the same tissues and there isn’t a clear border between them.

Cells in the colon or rectum sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous tumours such as hyperplastic and inflammatory polyps.

Changes to cells of the colon and rectum can also cause precancerous conditions. This means that the abnormal cells are not yet cancer, but there is a chance that they may become cancer if they aren’t treated. The most common precancerous conditions of the colon and rectum are adenomas and hereditary colorectal syndromes.

But in some cases, changes to colon or rectal cells can cause colorectal cancer. Most often, colorectal cancer starts in gland cells that line the wall of the colon or rectum. These gland cells make mucus that helps stool move through the colon and rectum. This type of cancer is called adenocarcinoma of the colon or rectum.

Rare types of colorectal cancer can also develop. These include small cell carcinoma and squamous cell carcinoma.

Expert review and references

  • American Cancer Society . Colorectal Cancer . 2018 : https://www.cancer.org/.
  • American Society of Clinical Oncology. Colorectal Cancer. 2017: https://www.cancer.net/cancer-types/colorectal-cancer/view-all.
  • Sundling KE, Zhang R, Matkowskyj KA . Pathologic features of primary colon, rectal, and anal malignancies. Bentrem D & Benson AB (eds.). Gastrointestinal Malignancies. Springer; 2016: 309-330.
  • Wilkes GM . Colon, rectal, and anal cancers. Yarbro CH, Wujcki D, Holmes Gobel B, (eds.). Cancer Nursing: Principles and Practice. 8th ed. Burlington, MA: Jones and Bartlett Learning; 2018: 51: 1423 - 1485.

The colon and rectum

The colon and rectum are parts of the large intestine. Learn about the colon and rectum, including their function.

Cancerous tumours of the colon or rectum

Cancerous tumours of the colon and rectum are growths that can spread to other parts of the body. Learn about adenocarcinoma and rare types of colorectal cancer.

Precancerous conditions of the colon or rectum

Learn about precancerous conditions of the colon and rectum that can increase the chance of developing colorectal cancer.

Non-cancerous tumours of the colon or rectum

Learn about non-cancerous tumours of the colon and rectum, such as hyperplastic polyps, that are not usually life-threatening.

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