2. Sudden weight loss
Unintentional weight loss of ten pounds or more within six months or less can be an early warning sign for many different types of cancer, including colorectal cancer. Weight loss occurs in combination with cancer because the presence of cancer cells can release substances into the body that change the way food is absorbed. Weight loss can also result from a blockage in the colon when the tumor has grown large enough, which will affect bowel movements and weight.