Colon Cancer

Colon cancer begins in the large intestine. Depending on where it starts, it is also sometimes called colorectal cancer or rectal cancer. The large intestine is the final part of the digestive (gastrointestinal, or GI) system and is made up of the colon and the rectum. The colon is the largest part of the large intestine and has four sections — the ascending, transverse, descending and sigmoid colon — with the sigmoid colon connecting to the rectum. Its main job is to absorb the remaining fluids and electrolytes from digested food before waste is passed out of the body as stool.

Colon cancer usually begins as polyps, benign clumps of cells that form in the inner lining of the colon. Over time, cancer can develop within a polyp and grow into the wall of the colon.

Colon cancer is the third most common cancer in the United States. It is the third leading cause of cancer-related deaths in both men and women, and the second most common cause of cancer deaths. The American Cancer Society estimated that in 2021 about 104,270 people in the United States would be diagnosed with colon cancer and about 52,980 would die from it.

Types of colon cancer

There are several types of colon cancer, depending on where they start.

• Adenocarcinomas: the most common type, which starts in the cells lining the inside of the colon.
• Carcinoid tumours: start in the hormone-making cells of the intestine.
• Gastrointestinal stromal tumours (GISTs): start in cells called the interstitial cells of Cajal in the wall of the colon; some of these tumours are benign.
• Primary colon lymphomas: start in immune cells called lymphocytes and may develop in the colon or rectum.
• Sarcomas: start in the blood vessels, muscle layers or other connective tissues in the wall of the large intestine.

Risk factors

Several factors can increase the risk of developing colon cancer:

• Age: the risk increases with age, and colon cancer most commonly develops after the age of 50.
• Race/ethnicity: African Americans are at higher risk.
• Personal medical history: people who have had colon cancer, polyps or inflammatory bowel disease are at higher risk.
• Inherited syndromes: about 5% of colon cancers are linked to inherited genetic mutations, the most common being Lynch syndrome (hereditary non-polyposis colorectal cancer, or HNPCC) and familial adenomatous polyposis (FAP).
• Family history of colon cancer.
• Diet: a diet low in fibre and high in fat and red meat is linked to an increased risk.
• Smoking: the risk is higher in smokers than in non-smokers.
• Obesity: being overweight or obese raises the risk.
• Diabetes: people with diabetes are at higher risk.
• Lack of physical activity: a sedentary lifestyle raises the risk.
• Previous cancer treatment: radiotherapy used to treat a previous cancer may increase the risk.

Signs and symptoms

Signs and symptoms of colon cancer may include:

• a change in bowel habits, such as persistent diarrhoea, constipation or a change in stool consistency
• rectal bleeding
• blood in the stool (dark brown or black in colour)
• persistent abdominal pain or discomfort
• a feeling that the bowel does not empty completely
• weakness and fatigue
• weight loss

How colon cancer is diagnosed

Diagnosis usually begins with a review of your medical history and a physical examination, followed by further tests and investigations such as:

• Stool test: a faecal occult blood test (FOBT) or faecal immunochemical test (FIT).
• Colonoscopy with biopsy.
• Blood tests.
• Imaging tests: CT, MRI and PET/CT scans may be used to find out whether the cancer has spread (metastasised) to other parts of the body.

Treatment options

After diagnosis, your doctor will establish the stage of the disease. Taking into account your current health, medical history and the results of staging, they will discuss the most suitable treatment options with you. Regular follow-up and periodic monitoring with tests and investigations are strongly recommended.

Treatment options include:

• Surgery is often used for early-stage colon cancer, and the type depends on the stage and location of the cancer:
• polypectomy: removing the polyp, along with the cancer, during a colonoscopy (for early-stage cancer).
• local excision: removing small cancers in the inner lining, along with a small amount of surrounding healthy tissue, during a colonoscopy (for early-stage cancer).
• hemicolectomy, partial colectomy or segmental resection: removing part of the colon and nearby lymph nodes, then reconnecting the remaining sections.
• total colectomy: removing all of the colon.
• Chemotherapy uses drugs, given intravenously or orally, to kill cancer cells throughout the body, and may be given before or after surgery:
• adjuvant chemotherapy: given after surgery to kill any remaining cancer cells and lower the chance of the cancer coming back.
• neoadjuvant chemotherapy: given before surgery, sometimes together with radiation, to shrink the tumour before it is removed.
• Radiotherapy uses high-powered energy beams to kill cancer cells and can be used before, during or after surgery. The two types used for colon cancer are external beam radiation therapy (EBRT) and brachytherapy.
• Targeted therapy uses drugs that act on specific abnormalities within cancer cells.
• Immunotherapy uses immune cells, or drugs that prompt the immune system, to kill cancer cells.
• Alternative treatments use other science-based approaches to attack cancer cells.

Reducing your risk

You can reduce your risk of colon cancer by:

• choosing a healthy diet
• limiting alcohol
• stopping smoking
• exercising regularly
• maintaining a healthy weight