What Is the Main Cause of Rectal Cancer?

Many types of rectal cancer are often detected during routine rectal examinations. Signs and symptoms usually develop later. Early symptoms may include:

• Blood in the stool (most common)
• Change in bowel habits (such as diarrhea, constipation, or increased bowel movements in a day)
• Narrow stool (due to the tumor obstructing the passage of stool)
• Feeling that the bowel doesn't empty completely

As rectal cancer progresses and spreads to other organs, patients may experience:

• Abdominal pain
• Unexplained weight loss
• Weakness
• Fatigue

Blood in the stool (or bleeding) and a change in usual bowel habits are usually the main symptoms that point toward the diagnosis of rectal cancer, particularly if the patient is elderly. The patient should schedule an appointment with their doctor to know if rectal cancer is causing these symptoms. Earlier testing improves the outcome of cancer treatments.

Rectal cancer is most often detected as a hard mass during routine rectal examinations known as digital rectal exams (DRE). During DRE, the doctor inserts fingers into the patient’s rectum to feel it. They take the patient’s complete medical history and perform a physical exam. To check if the mass is cancerous, the doctor will perform procedures such as:

• Proctoscopy: In this test, the doctor inserts a proctoscope (a hollow tube) through the patient’s anus to visualize their rectum. This is usually done at the doctor’s office and does not involve any special preparation before the procedure.
• Colonoscopy: In this procedure, the doctor inserts a colonoscope (a long, flexible tube) into the patient’s rectum to look for changes such as polyps and any other abnormal growth in the rectum and colon. This is a hospital-based procedure that needs special preparations such as taking a laxative the night before.
• Biopsy: The doctor will remove a piece of the patient’s rectum during a colonoscopy. They will send the sample of the rectum to the laboratory to check for the presence of cancerous cells. This test known as a biopsy provides a definitive diagnosis of rectal cancer.

Once rectal cancer has been diagnosed, the doctor performs certain tests to know the extent of cancer and the stage, which include:

• Blood tests
  • Complete blood count (CBC)
  • Liver function tests
  • Kidney function tests
  • Carcinoembryonic antigen (CEA, a tumor marker that may be higher than usual if a patient has colorectal cancer)
• Computed tomography (CT) scan of the chest (to check if cancer has spread to the liver or lungs)
• Magnetic resonance imaging (MRI) of the pelvis (to get a detailed view of the structure of the rectum)

Rectal cancer is categorized from stages 0-IV based on how far the tumor has spread and whether it has spread beyond the rectum. This can be confirmed via imaging tests such as MRI or CT scans and biopsy. 

• Stage 0: Cancer cells have been found on the surface of the rectal lining or rectal mucosa.
• Stage I: The tumor has grown below the rectal mucosa and has possibly extended into the rectal wall.
• Stage II: The tumor has grown into the rectal wall and may extend into tissues around the rectum.
• Stage III: The tumor has spread to the lymph nodes located next to the rectum and some tissues beyond the rectal wall.
• Stage IV: The tumor has spread to distant lymph nodes or organs.

The survival rate of a rectal tumor depends on the stage of the tumor at the time of diagnosis. Overall, survival rates of rectal cancer are fair at 67%. If detected at an earlier stage, rectal cancer is curable and can be prevented from progressing to later stages.

Survival rates are analyzed in a large study, in which the lifespan of a large population after a cancer diagnosis is observed for a specific timeframe. It is generally presented as a 5-year survival rate—the percentage of people who lived for at least 5 years after a diagnosis.

For example, the 5-year survival rate (as shown in the table below) for rectal cancer limited only to the rectum (localized tumor) is 90%. This means that 90 of 100 people who were diagnosed with rectal cancer in an earlier stage may live for at least 5 years or more.

^{*SEER stage: Stage of the tumor as determined by the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute. These numbers are derived from data obtained between 2011 and 2017.}