Colorectal cancer occurs when tumors form in the lining of the large intestine. It is common in both men and women. The risk of developing colorectal cancer rises after age 50. .
Nearly 20,000 new cases of colorectal cancer were expected in the United States among African Americans in 2019, with incidence rates 24 percent higher in black men and 19 percent higher in black women compared to other races, according to the American Cancer Society. Black colorectal cancer patients are also 15 to 20 percent more likely to die from the disease than patients of any other race.
Colorectal cancer, also known as bowel cancer, colon cancer, or rectal cancer, is any cancer that affects the colon and rectum. The American Cancer Society (ACS) expects to see around 104,270 new cases of colon cancer and 45,230 new cases of rectal cancer in the United States in 2021. Colorectal cancer starts in the colon or the rectum. These cancers can also be called colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common. Cancer starts when cells in the body start to grow out of control.
The colon and rectum
To understand colorectal cancer, it helps to know about the normal structure and function of the colon and rectum.
The colon and rectum make up the large intestine (or large bowel), which is part of the digestive system, also called the gastrointestinal (GI) system (see illustration below).
Most of the large intestine is made up of the colon, a muscular tube about 5 feet (1.5 meters) long. The parts of the colon are named by which way the food is traveling through them.
- The first section is called the ascending colon. It starts with a pouch called the cecum, where undigested food is comes in from the small intestine. It continues upward on the right side of the abdomen (belly).
- The second section is called the transverse colon. It goes across the body from the right to the left side.
- The third section is called the descending colon because it descends (travels down) on the left side.
- The fourth section is called the sigmoid colon because of its “S” shape. The sigmoid colon joins the rectum, which then connects to the anus.
How do the colon and rectum work?
The colon absorbs water and salt from the remaining food matter after it goes through the small intestine (small bowel). The waste matter that’s left after going through the colon goes into the rectum, the final 6 inches (15cm) of the digestive system. It’s stored there until it passes through the anus. Ring-shaped muscles (also called a sphincter) around the anus keep stool from coming out until they relax during a bowel movement.
How does colorectal cancer start?
Polyps in the colon or rectum
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 turning into cancer depends on the type of polyp it is.
Nearly 20,000 new cases of colorectal cancer were expected in the United States among African Americans in 2019, with incidence rates 24 percent higher in black men and 19 percent higher in black women compared to other races, according to the American Cancer Society.