What Is the Main Cause of Rectal Cancer?

The rectum is the terminal part of the large intestine.

The rectum is the terminal part of the large intestine. The function of the rectum is to store feces till they are expelled from the body. Rectal cancer usually develops over years. Doctors do not know precisely what causes it.

Rectal cancer begins when changes (mutations) in the DNA of the rectal cells cause the cells to multiply and grow uncontrollably. The abnormal cells thus formed accumulate to form a harmful (malignant) tumor known as rectal cancer.

Certain factors increase the risk of rectal cancer, which include

• Older age
• Family history of colon or rectal cancer
• Rectal polyp (fleshy, abnormal growth on the rectum lining)
• Inflammatory bowel diseases such as Crohn’s and ulcerative colitis
• Hereditary syndromes
  • Lynch syndrome
  • Familial adenomatous polyposis (FAP)
• A diet low in fruits and vegetables
• High-fat diet (particularly animal fat)
• Lack of physical activity
• Smoking
• Alcohol drinking
• Radiation therapy for a previous cancer
• Human papillomavirus (HPV) infection
• Night shift work (more research is needed to prove the link)
• Cholecystectomy or removal of the gallbladder (more research needed to prove the link)

What are the signs and symptoms of rectal cancer?

Many types of rectal cancer are often detected during routine rectal examinations. Signs and symptoms develop later. The earlier ones include

• Blood in the stool (most common symptom)
• A 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)
• A feeling that 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.

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How is rectal cancer diagnosed?

Rectal cancer is most often detected as a hard mass during routine rectal examinations known as digital rectal exam (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 a 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 the 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 stage it, 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 viewed of the structure of the rectum)