Colorectal cancer is a malignant tumor found in the colon or rectum. The colon and the rectum are parts of the large intestine, which is part of the digestive system. Because colon cancer and rectal cancer have many features in common, they are sometimes referred to together as colorectal cancer. Excluding skin cancers, colorectal cancer is the third most common cancer in both men and women. The number of deaths from colorectal cancer has decreased, which is attributed to increased screening and polyp removal. This article focuses on adenocarcinoma, a type of cancer that accounts for more than 95% of colorectal cancers. This cancer often starts as small polyps that continue to grow and can turn into malignant tumors. The exact cause of most colorectal cancer is unknown, but there are several risk factors. Two that you can't control are age and race: most people who have colorectal cancer are older than 50, and African-Americans have the highest risk. Certain medical conditions can increase the risk for this cancer: polyps, which are benign growths on the wall of the colon or rectum; ulcerative colitis, or Crohn's disease; type 2 diabetes; and inherited syndromes, such as familial adenomatous polyposis or hereditary nonpolyposis colon cancer. Health history makes a difference as well. The risk is higher for people who have had precancerous polyps and for people with a strong family history of colorectal cancer or polyps. Last but not least, certain lifestyle habits can increase your risk. Colorectal cancer is often associated with a diet high in red and processed meats. Obesity, physical inactivity, heavy alcohol consumption, and smoking all play a role as well. Tests that may help find or diagnose colorectal cancer may include: Digital rectal examination: A health care provider inserts a gloved finger into the rectum to feel for anything unusual. This test can detect cancers of the rectum but not cancers in the colon. It is not useful as a screening test for colorectal cancer. Fecal occult blood test (FOBT): This test checks for hidden blood in the stool. It involves placing a very small amount of stool on a special card, which is then tested in the doctor's office or sent to a laboratory. Fecal immunochemical test (FIT): This test is similar to a fecal occult blood test, but does not require any restrictions on diet or medications before the test. Sigmoidoscopy: A short, flexible, lighted tube, called a sigmoidoscope, is inserted into the lower part of the large intestine through the rectum. The doctor can see the lining of the lower portion of the colon and may remove tissue for examination. Colonoscopy: This test involves inserting a colonoscope, a long, flexible, lighted tube, through the rectum along the entire length of the colon. The doctor can see the lining of the colon, remove any abnormal tissue for examination, and possibly treat some problems that are discovered. Barium enema: A fluid called barium is inserted in the rectum to partially fill up the colon. An X-ray of the abdomen can highlight the presence of tumors or reveal narrowed areas, blockages, and other problems. CT colonography (virtual colonoscopy): This procedure uses computerized tomography (CT) to examine the colon for polyps or masses using special technology. The images are processed by a computer to make a three-dimensional model of the colon. Virtual colonoscopy is noninvasive, although it requires a small tube to be inserted into the rectum to pump air into the colon. Stool DNA (sDNA): This test is used to check the stool or fecal matter for specific changes in DNA, the genetic blueprint of each cell, that indicate signs of colorectal cancer. For this test, you must save an entire bowel movement and send the sample to a laboratory. Biopsy: Tissue samples are removed for examination to determine if cancer or other abnormal cells are present. This is usually done as part of a colonoscopy or sigmoidoscopy. Blood count: This test checks for anemia, a result of chronic bleeding from a tumor. It's possible to prevent many colorectal cancers through screening. Tests that may be used for screening are the FOBT, FIT, colonoscopy, sigmoidoscopy, barium enema, virtual colonoscopy, and the sDNA. Finding colorectal cancers early is the best way to improve the chances of successful treatment. Your doctor can explain which screening options may be right for you. When colorectal cancer is diagnosed, testing determines how much cancer is present and if it has spread to other parts of the body. This is called staging. Imaging tests such as a CT scan or MRI of the abdomen may be done to look for tumors to help determine the extent (stage) of the cancer. Staging is an important step toward planning a treatment program, which may include surgery, radiation therapy, chemotherapy, and/or targeted therapy.