Rectal Cancer Overview

What Causes Rectal Cancer, and How It Is Diagnosed and Treated

film showing rectum lit up in large intesting suggestive of cancer
What is rectal cancer, what are the symptoms, how is it diagnosed, and how is it treated?. Credit: Istockphoto.com/Stock Photo©janulla

What is rectal cancer? Is it the same thing as anal cancer or colon cancer? What causes rectal cancer? What are the symptoms and how is it treated?

These are common questions that relate to rectal cancer. Learn the answers to these questions and others, below. 

Definition 

Rectal cancer is a type of cancer that develops in the rectum, the last six inches of the large intestine. Like other organs in the body, the rectum is vulnerable to many diseases and conditions, such as cancer.

Rectal cancer differs from ​anal cancer, which refers to cancers that are in the region between the rectum and the outside of the body. The terms colon cancer and colorectal cancer are often used interchangeably, so much of the information that you will see about colon cancer pertains to rectal cancer, as well. But rectal cancer is different from cancer that is found higher up in the colon, especially when it comes to treating the disease with surgery. 

Since rectal cancer and cancers that are higher up in the colon are often lumped together, it's hard to know the exact incidence of rectal cancer, specifically. But colon cancer is the third leading cause of cancer deaths in men and the third leading cause of cancer deaths in women in the United States. This diagram shows the location of the rectum within the large intestine. 

Causes and Risk Factors

Scientists don't know exactly what causes rectal cancer, but they do know what increases a person's risk of developing it.

Risk factors for rectal cancer include:

  • Being older than 50.
  • A family or personal history of colon cancer. But keep in mind: A person does not need a family history of colon cancer to have rectal cancer; it is most commonly diagnosed in those without a family history. It's thought that 25% of colon cancers have a genetic link.
  • A personal history of some types of colon polyps (small growths in the colon).
  • Smoking—either currently or in the past.

Symptoms

In its early stages, rectal cancer usually doesn't have symptoms. As the disease progresses, which can take years, symptoms of rectal cancer include:

  • Blood in stool: This is often bright red, versus blood in the stool that's related to cancers that are higher in the colon (blood due to those types of cancers can appear dark red or black).
  • Digestive issues: Persistent constipation, diarrhea, or other bowel changes.
  • Thinner stools: Stools that are described as "pencil like" or thin may occur when a tumor in the rectum obstructs part of the canal.
  • Unexplained weight loss: Unintentional weight loss defined as the loss of at least 5% of body weight over a six-month to 12-month period, can be a symptom of rectal cancer.
  • Abdominal Discomfort: This may include pain, tenderness, or cramping.
  • Generalized fatigue: You feel more tired than usual, even if you're sleeping well. 
  • Anemia: When rectal cancer causes chronic, light bleeding, the first symptom may be anemia or symptoms related to anemia such as lightheadedness, fatigue, or pale skin.

Screening

Several colon cancer screening methods are highly effective at detecting rectal cancer, as well.

Colon and rectal cancer screening tests include:

  • Colonoscopy: A colonoscopy allows the doctor to get an in-depth view of the colon with a colonoscope, a fiber-optic tube that is attached to a microscopic camera that transmits live video to a monitor. The colonoscope is gently inserted into the anus and slowly into the colon, giving the doctor a full view of the rectum and large intestine.
  • Sigmoidoscopy: Much like a colonoscopy, a sigmoidoscopy is done with a flexible, lighted tube with an attached camera, but it is limited to only the lower part of the colon.
  • Barium Enema: During a barium enema, a doctor inserts liquid barium into the rectum. X-rays are taken of the patient while he or she lies in several different positions. The barium allows the colon to be viewed better on x-rays.
  • Fecal Occult Blood Test: A fecal occult blood test (FOBT) finds blood in your stool that you may not see with the naked eye or confirms that it is actually blood in the stool that you may have seen. You are given a special kit to collect stool samples.

For adults who are at average risk of developing colon or rectal cancer, it is recommended to begin getting screened at age 50. Adults who are at a higher risk of developing the disease may need to begin screening at an earlier age at the recommendation of their doctor. Remember: Even if you are not experiencing any symptoms of rectal cancer, you should always follow your doctor's screening recommendations.

Diagnosis 

If a screening test reveals suspicious results, then a colon biopsy is done. A colon biopsy can be done during a colonoscopy or surgery. During a colon biopsy, small amounts of rectal tissue are removed and then sent to a pathology lab to screen for evidence of cancer. If cancer is present, then the stage of rectal cancer is determined during surgery that's performed to remove the cancer. Surrounding lymph nodes are tested and may also be removed during the surgery.

Further testing may be done to see whether the cancer has metastasized or spread. 

Treatment 

The treatment for rectal cancer will depend upon the stage of the disease, as well as other factors such as the particular location of the tumor(s) and your general health.

Surgery: In the early stages of rectal cancer, surgery may be the only treatment needed. There are several surgical methods that are used to remove cancerous rectal tissue. The type of surgery that's chosen depends on the patient's general health, the stage of the rectal cancer, and the location of the tumor(s). For those who are not good candidates for surgery, radiation therapy may be an option, but it is usually not as effective.

Chemotherapy: This is also a common treatment for rectal cancer. The organs in the body are made up of cells that divide and multiply as the body needs them. When these cells continue to multiply unnecessarily, the result is a mass or growth, which is also called a tumor. Chemotherapy drugs work by eliminating these rapidly multiplying renegade cells. ​Chemotherapy for rectal cancer may be prescribed either before or after surgery and may also be given in conjunction with radiation therapy.

Radiation therapy: This is another treatment option for rectal cancer. This type of therapy uses certain types of high-energy radiation beams to shrink tumors and eliminate cancer cells. Radiation therapy works by damaging a cancer cell's DNA, making it unable to multiply. In cases of rectal cancer, radiation therapy may be given prior to surgery to help shrink large tumors. It may also be given in conjunction with chemotherapy.

Prevention

Regular colon cancer screening is key to preventing rectal cancer. Screening can identify precancerous growths before they potentially progress into cancer. Keep in mind that it takes years for rectal cancer to develop, so routine screening can detect these changes long before they turn cancerous. 

Avoiding risk factors for colon cancer can also reduce your chances of developing the disease. Eating a balanced diet is important, as well as maintaining a healthy weight and quitting smoking.

Sources:

American Cancer Society. Colorectal Cancer. Updated 01/20/16. http://www.cancer.org/cancer/colonandrectumcancer/detailedguide/colorectal-cancer-risk-factors

National Cancer Institute. Rectal Cancer Treatment – for Health Professionals PDQ). Updated 01/29/16. http://www.cancer.gov/types/colorectal/hp/rectal-treatment-pdq

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