Colorectal cancer is a type of cancer where abnormal cells form in the colon or rectum. Cancers of the colon and cancers of rectum are often grouped together because the colon and rectum share common features as parts of the gastrointestinal system.

The vast majority of colorectal cancers forms in the mucus-producing glands (adenocarinomas) inside the colon or rectum and develop over several years. They usually start as small, benign (noncancerous) clumps of cells in the colon known as polyps.

While showing few symptoms, polyps can eventually become cancerous. It is mainly for this reason that doctors recommend regular screenings to find polyps before they become cancerous.

Less common tumors that can form in the colon or rectum are gastrointestinal stromal tumors and lymphomas.

The National Cancer Institute estimates there will be more than 142,500 new cases of colorectal cancer and more than 51,300 colorectal cancer-related deaths by the end of 2010.

Symptoms

As colorectal cancer develops, it could include these symptoms: 

  • fatigue
  • rectal bleeding
  • blood in stool
  • abdominal pain
  • gas
  • unexplained weight loss
  • a feeling that your bowel doesn't completely empty
  • changes in bowel habits, such as diarrhea or constipation

Risk Factors

Besides polyps, inherited gene mutations can also increase your risk for cancer. Other risk factors include:

  • being over the age of 50
  • being African-American
  • inflammatory bowel disease
  • smoking, obesity
  • a diet low in fiber and high in fat
  • diabetes
  • radiation for treatment of other cancers

Colorectal cancer spreads—or metastasizes—when cancerous cells invade the blood or lymph vessels and are carried to other parts of the body, such as the infection-fighting lymph node system or liver.

Prognosis

If you've been diagnosed with colorectal cancer, your treatment options vary and will depend on the stage of the cancer. The three primary treatments are surgery, chemotherapy, and radiation therapy. For early-stage colorectal cancer, where the cancer is isolated in a polyp, a small surgical procedure during a colonoscopy may be able to completely remove all cancerous cells. Larger polyps may be removed using laparoscopic surgery. For a more invasive colorectal cancer, your doctor might recommend any of the following:

  • Colectomy is a surgery to remove the part of the colon containing the cancer, as well as some nearby tissue.
  • Local excision of the rectum is the removal of cancerous portions of the rectum.
  • Resection is a procedure used if cancer has spread into the walls of the rectum. In it, the cancerous section of the rectum is removed, along with some nearby healthy tissue.
  • Pelvic exenteration is the removal of the lower colon, rectum, and bladder as well as the prostate in men and the cervix and ovaries in women. This procedure is used only if cancer has spread to these other organs.

For some advanced colorectal cancers, chemotherapy or radiation therapy may be used before or after surgery. When used before surgery, these treatments are meant to shrink tumors so that they are more easily removed. When used after surgery, these treatment options are meant to destroy any remaining cancer cells, control tumor growth, or to relieve symptoms of colorectal cancer. 

View the Colorectal Cancer Learning Center for more information.