What is colorectal cancer?

Cancer is a disease characterized by the unchecked division of abnormal cells. When this type of growth occurs in the colon or rectum, it is called colorectal cancer (CRC). The colon and rectum (colorectum), along with the anus, make up the large intestine, the final segment of the gastrointestinal (GI) system. The large intestine is sometimes called the large bowel, which is why CRC is sometimes referred to as bowel cancer. The function of the large intestine is to absorb water and electrolytes from food matter and eliminate feces. As depicted in Figure 1, the first part of the large intestine is the colon, a muscular tube about 1.5 meters (5 feet) long and 5 centimeters (2 inches) in diameter that is divided into 4 sections: • The ascending colon begins with the cecum (a pouch where undigested food is received from the small intestine) and extends upward on the right side of the abdomen.

• The transverse colon crosses the body from right to left, and is referred to collectively with the ascending colon as the proximal, or right, colon.

• The descending colon descends on the left side.

• The sigmoid colon, named for its “S” shape, is the final portion of the colon and is referred to collectively with the descending colon as the distal, or left, colon.