Colon cancer is a type of cancer that begins in the large intestine. The colon is the final part of the digestive tract. Colon cancer typically affects older adults, though it can happen at any age. It usually begins as small, noncancerous 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. Colon cancer is sometimes called colorectal cancer, which is a term that combines colon cancer and rectal cancer, which begins in the rectum. Symptoms A persistent change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool Rectal bleeding or blood in your stool Persistent abdominal discomfort, such as cramps, gas or pain A feeling that your bowel doesn’t empty completely Weakness or fatigue Unexplained weight loss Causes In general, colon cancer begins when healthy cells in the colon develop changes in their DNA. A cell’s DNA contains a set of instructions that tell a cell what to do. Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell’s DNA is damaged and becomes cancerous, cells continue to divide even when new cells aren’t needed. As the cells accumulate, they form a tumor. With time, the cancer cells can grow to invade and destroy normal tissue nearby and cancerous cells can travel to other parts of the body to form deposits there.