context: You've probably heard of âcolorectal cancer,â but colon cancer and rectal cancer aren't the same. If you or someone you're close to has it, you'll want to know what they have in common and how they differ. It's important to know which one you have. That will affect your treatment options and what you can expect -- or as doctors say, your prognosis. Both colon and rectal cancer affect the large intestine, which is the lowest part of the digestive system. But they start in different places within it. Colon cancer can start anywhere in the colon, which is about 5 feet long and absorbs water from stool. Rectal cancer starts in the rectum, which is the last 12 centimeters (nearly 5 inches) of the colon. It's where the body stores stools until you have a bowel movement. The location also matters because of what's nearby. Most of the colon is in the large space between the bottom of your ribcage and your pelvis. The rectum is in a more crowded neighborhood. Your bladder is nearby. So are the uterus and vagina for women, or the prostate for men. The tight space may affect the kinds of surgeries that doctors can do to remove tumors. Both colon and rectal cancer are likely to cause many of the same symptoms, including: Stomach or gas pains Constipation or diarrhea Black, dark, or red colored stools, which can all indicate blood Feeling weak or tired Doctors also use the same approach to diagnose both types of colorectal cancer. You'll likely get a colonoscopy. In this procedure, a doctor uses a long, thin, flexible tube to see the inside of your rectum and colon. If they see areas that could have cancer, the doctor can remove small samples called biopsies to test. Many people have small growths in the colon, called polyps, which aren't cancerous but may need to come out before they become a problem. The first treatment for colon cancer is usually surgery to remove a section of the colon. Your doctor will call this operation a partial colectomy. Most often, doctors can reconnect the separated sections of the colon after the surgery and you'll have normal bowel movements again. But sometimes, that can't happen. In those cases, you'll have an operation called a colostomy. Your surgeon will connect the colon to a hole in your abdomen, called an ostomy. You'll have a bag that attaches to the ostomy to collect bowel movements. If your colon cancer has spread to the lymph nodes or affects a thick section of the colon, your doctor may recommend chemotherapy to kill cancer cells. For rectal cancer, surgery is the main treatment if doctors can completely remove your tumor. You may also get chemotherapy and radiation therapy to kill any remaining cancer cells or to shrink a tumor before surgery. During operations for rectal cancer, your surgeon will try to cut out any tissue affected by cancer without removing the anal sphincter muscle, which controls the opening and closing of the anus during bowel movements. But in some cases, a rectal tumor is too close to the muscle to save it. In that case, you'll need a colostomy. It's rare to need a colostomy after colon cancer surgery. But about 1 in 8 people with rectal cancer needs an ostomy, according to the National Cancer Institute.