Colon and rectal cancer develop in the digestive system, which is also called the gastrointestinal, or GI system. Colorectal cancers are thought to develop slowly over a period of several years. We now know that most colorectal cancers begin as a polyp, also known as an adenoma. Over about 5 to 10 years adenomas can slowly change into cancer. A polyp is a mass of tissue that grows into the center of the intestine.
Colon adenoma-polyp
Once a cancer forms in these polyps it will grow into the center of the colon or rectum. It will also grow into the wall of the colon or rectum. Once in the wall, the cancer cells can grow into blood vessels, lymph vessels and than spread to other parts of the body. This process is called metastasis. Over 95% of colorectal cancers are adenocarcinomas.
Colon cancer
            
              

         
             Stages of colon (rectal) cancer


  1. Stage 0: Since your cancer has not grown beyond the inner lining of the colon, surgery to take out the cancer is all that is needed.
  2. Stage I: Your cancer has grown through several layers of the colon. But it has not spread outside the colon wall itself. Surgical resection to remove the cancer is the standard treatment. You do not need any additional therapy.
  3. Stage II: Your cancer has grown through the wall of the colon and may extend into nearby tissue. It has not yet spread to the lymph nodes. Surgical resection is usually the only treatment you need. If your doctor thinks your cancer is likely to come back because of its appearance under the microscope or because it was growing into other tissues, radiation or chemotherapy may be recommended.
  4. Stage III: This is a more advanced stage. Your cancer has spread to nearby lymph nodes. But, it has not yet spread to other parts of the body. Surgical resection is the first treatment. You should then receive chemotherapy and radiation treatment (rectal cancer).
  5. Stage IV: In this stage the cancer has spread to distant organs and tissues such as the liver, lung, peritoneum, or ovary. The goal of surgery in this stage is usually to relieve or prevent blockage of the colon and to prevent other local complications (bleeding etc.). If your metastases can't be removed, chemotherapy is the main treatment. It may also be possible to destroy the tumors by freezing, heating with microwaves, or other nonsurgical methods.



                    Treatment options
       

       After the cancer has been found and staged, your doctor will recommend one or more treatment options. The 3 main types of treatment for colon cancer and rectal cancer are surgery, radiation therapy, and chemotherapy. Depending on the stage of the cancer, 2 or even 3 of these types of treatment may be combined.

  • Surgery is the main treatment for colon and rectal cancer. The usual operation is called a segmental resection-colectomy. During this surgery, the cancer and a length of normal tissue on either side of your cancer as well as the nearby lymph nodes are removed. The remaining sections of your colon are then re-attached. A colon resection rarely causes any major problems with digestive functions and you should be able to eat in a few days. If the tumor is large and has blocked your colon, or it has punched a hole in your colon so wastes have leaked out, a temporary ( 10-12 weeks) colostomy may be needed. Rarely, if your tumor can’t be removed, you may need a permanent colostomy.
  • Chemotherapy after surgery can increase the survival rate for patients with some stages of colon cancer and rectal cancer. This is called adjuvant (additional) chemotherapy.
  • Radiation therapy is treatment with high-energy rays that destroy cancer cells. After surgery for rectal cancer, radiation can kill small deposits of cancer that may not be seen during surgery. If a rectal cancer's size and/or position makes surgery difficult, radiation may be used before surgery to shrink the tumor.


Can Colon and Rectal Cancer Be Prevented?

      Prevention and early detection are possible because most colon cancers develop from adenomatous polyps. Polyps are precancerous growths in the colon and rectum. Removing them can lower a person's cancer risk.
     Screening tests are used to spot a disease early even if you do not have symptoms or a history of that disease. Screening for colorectal cancer not only can find it at an early curable stage, it can also prevent it by finding and removing polyps that might have become cancer. Cancers can also be found early if you report any symptoms right away to your doctors, but being screened before symptoms occur is better. There are several tests used to screen for colorectal cancer. used
  1.  Fecal occult blood test
  2.  Sigmoidoscopy
  3.  Colonoscopy
  4.  Barium enema with air contrast