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Colorectal Cancer

Cancer is when cells grow out of control. The cells form a clump of tissue called a growth or tumor. Cancer cells can invade nearby tissues. It can then spread to other parts of the body.

A tumor can be benign or malignant. A benign tumor is not cancer and will not spread to other parts of the body. In the colon (large intestine), most benign growths are called polyps.

A malignant tumor is cancer. Cancer cells invade and damage tissue around them. They can also enter the lymph and blood streams, spreading to other parts of the body. Colorectal cancer is the growth of malignant cells in the colon.

Cancer Cell Growth
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Normal Anatomy and the Development of Colorectal Cancer

The colon is the last part of the gastrointestinal tract. This tract is where food is taken in and digested for the body to use. The colon's main job is to absorb water and salt from solid waste before it is passed from the body as stool (poop). The rectum is next. It stores stool until it is ready to be passed from the body through the anal canal.

Cell growth and death are normal processes in the body to replace old or damaged cells. The walls of the colon have cells that die and are replaced faster because of the digestive process. The colon may also be exposed to carcinogens, or things that can cause cancer. These carcinogens may come from waste expelled from the body, food breakdown, and gut bacteria. They can cause damage to cells in the colon. This can lead to a high level of cell turnover. Places where there are rapid changes like this are more at risk for cancer forming.

Polyps are another thing that can lead to cancer forming. Polyps are small growths that can be found in the colon and rectum. There are several types. Most are benign, but some can turn into cancer. The highest risk of cancer development comes from adenomatous polyps.

Cancer can happen anywhere in the colon, but it is most commonly found in the last section. Colorectal cancer may cause bleeding or make it hard for the colon to work as it should.

If the cancer grows beyond the colon or rectum, it can spread into nearby places, such as the urinary tract, reproductive organs, or anus. It can make it hard for these organs to work as well and cause issues such as problems passing urine.

It can also spread to lymph nodes or blood vessels, which can carry cancer cells to other parts of the body. The most common sites for colorectal cancer to spread to are lymph nodes in other parts of the body, the lungs, liver, or other organs in the belly and pelvic areas.

Types of Colorectal Cancer

The wall of the large intestine is made of four layers. From the innermost to outermost layer, they are named mucosa, submucosa, muscle, and serosa. Almost all colorectal cancers are . That is, they start in the mucosa and spread outward through the serosa. Other types include:

  • —these form from the hormone-producing cells of the intestinal tract
  • —these form from special cells in the colon wall, but can be found anywhere in the GI tract
  • —these are rare and form from the muscular tissue of the intestine
Colon Cancer
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Rectal Cancer
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  • Benson, A.P., Venook, A.B., et al. Colon Cancer. Version 2.2017 NCCN Clinical Practice Guidelines in Oncology. Journal of the National Comprehensive Cancer Network, 2017; 15 (3): 370-398.
  • Colon cancer treatment option overview. National Cancer Institute website. Available at: https://www.cancer.gov/types/colorectal/patient/colon-treatment-pdq#section/%5F135.
  • Colorectal cancer. American Cancer Society website. Available at: http://www.cancer.org/acs/groups/cid/documents/webcontent/003096-pdf.pdf.
  • Colorectal cancer. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/colorectal-cancer.
  • Glynne-Jones, R., Wyrwicz, L., et al. Rectal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology, 2017; 28 (suppl%5F4): iv22-iv40.