Colon cancer forms in the tissues of the large intestine, the lower part of the digestive system. It is one of the more common cancers and a leading cause of death in the United States. In 2009, there were 106,100 cases of colon cancer and 49,920 deaths from colon and rectal cancer, according to the National Cancer Institute. Treatment for colon cancer includes surgery, chemotherapy, biotherapy and radiation. Complications may occur from treatment side effects and disease progression.

Complications of Treatment

Bleeding and infection after surgery, urinary retention, leakage from the surgical site, and pain may occur after surgery. Complications from chemotherapy and biotherapy depend on the agents used, but may include:

• nausea
  
• vomiting
  
• diarrhea
  
• inability to fight infection
  
• allergic reactions

Radiation therapy may cause skin reactions or burns, mechanical blockages (strictures), bleeding and radionecrosis (tissue destruction due to the radiation energy).

Intestinal Obstruction

Intestinal obstruction or blockage in the colon occurs when waste products (feces) are unable to move through the intestine. Causes include mechanical blockage such as scar tissue from surgery or radiation, cancer progression (metastasis), or an ileus where no mechanical blockage exists but the intestine is unable to contract and relax.

Recurrence

Recurrence, or the return of the cancer after a period of time, happens when surgery does not remove the primary tumor completely or hidden cancer cells remain. Local (site of the original tumor), regional (in the lymph nodes near the primary tumor) or distal (in another part of the body) recurrence may occur. For example, the patient seems to be cancer free for a year and then the cancer returns. Progression of the disease is said to occur when the tumor grows during treatment (usually in the first few months), which indicates an aggressive type of tumor.

Metastasis

Cancer cells that break away from the primary tumor and travel in the blood stream or lymph system to other parts of the body cause metastases. These new sites of disease are still colon cancer, even when they are in other organs of the body. Metastasis in colon cancer usually is seen in the liver and lungs but may occur in other sites.

Development of a Second Primary Cancer

When a second primary colon cancer develops, it is said to be metachronous colon cancer 1. Metachronous colon cancer is described as a cancer that develops six or more months after the primary tumor and is often in another site 1. Because colon cancer often develops from polyps (or growths) in the colon, a second primary cancer may occur.