What to know about colon cancer stages Despite the fact that colorectal cancer cases have been declining in the United States since the mid-1980s, it is still the third most common cancer diagnosed each year excluding skin cancer. Often shortened to colon cancer, colorectal cancer occurs when cells in the colon and/or the rectum begin to grow uncontrollably and eventually spread to other parts of the body. One important tool when understanding a colon cancer diagnosis is learning about the...