Colorectal cancer refers to the presence of malignant cells in the colon or rectum. Colon cancer and rectal cancer are grouped together because the tissue of the two organs is similar, and there is not a clear demarcation between them.
Changes within the colon or rectum can result in precancerous conditions, including adenomas and hereditary colorectal syndromes. Cancer most often develops in the mucous glands of the colon and rectum, resulting in adenocarcinoma. In rare cases, small cell carcinoma and squamous cell carcinoma can develop in the colon or rectum.
Who Is at Risk for Colorectal Cancer?
Colorectal cancers are quite common. The Canadian Cancer Society estimates that over 24,000 Canadians were diagnosed with colorectal cancer in 2022, and the disease led to 94,000 deaths. It is the fourth most common cancer diagnosis in Canada.
Colorectal cancer is more common in men than women. One in 14 Canadian men will develop colorectal cancer in their lifetime, compared to 1 in 18 women.
Age is a risk factor for colorectal cancers. Most cases are diagnosed in people over 40 years old, with incidence numbers rising in every decade of life after that.
Other risk factors for colorectal cancer include:
- Family history of colorectal cancer or precancerous conditions
- Personal history of cancer such as breast, ovarian, and uterine cancer
- Inflammatory bowel disease
- Ashkenazi Jewish ancestry
- Lifestyle factors such as excessive weight, a diet high in processed meats, smoking, alcohol consumption, or sedentary behaviour
What Are Current Treatments for Colorectal Cancer?
Treatment varies by the stage and location of the cancer cells. The most commonly prescribed treatment protocols include:
- Radiofrequency ablation
- Radiation therapy
- Targeted therapy
Surgery is typically the first line of treatment regardless of stage. Excision is often possible with local tumours, with surgery, ablation, or cryosurgery. Resection of the colon with anastomosis is used for larger tumours. In some cases, patients require resection of the colon with colostomy.
Follow-up treatment may be necessary when cancer has spread or surgery cannot remove all tumour cells. Rectal cancer has a higher likelihood of recurrence, so additional treatment and monitoring after surgery are often recommended. Chemotherapy may be offered after surgery if there is a high risk that the cancer will recur and at least one of the following high-risk features is present:
- The tumour is T4 (stage 2B or 2C)
- Fewer than 12 lymph nodes were removed or could be assessed
- The tumour has grown into nearby lymph nodes, blood vessels or the space surrounding nerves
- The tumour is high grade
- There is a blockage in the intestine (bowel obstruction) or a tear or hole in the intestine (bowel perforation)
- Not enough healthy tissue was removed along with the tumour, or cancer cells are found in the tissue removed with the tumour
New and Recent Studies on Colorectal Cancer
In recent years, research has focused on the screening and prevention of colorectal cancers. New screening methods such as fecal immunochemical tests (FIT), stool DNA testing, and blood tests to detect biomarkers related to colorectal cancer have shown promise. Less invasive imaging tests like CT colonography and capsule endoscopy are alternatives to traditional colonoscopy.
Researchers have developed immunotherapies such as monoclonal antibodies and immune checkpoint inhibitors that provoke the immune system to attack cancer cells. Investigators are studying whether existing targeted therapy drugs are effective against colorectal cancers.
Importance of Early Screening
Colorectal cancer screenings allow doctors to identify precancerous changes and remove the abnormal cells before cancer can develop. Screening can also help identify cancer in earlier, more localized stages when treatment is easier. About 67 percent of people diagnosed with colorectal cancer will survive for at least 5 years after their diagnosis.
What Are the Early Symptoms and Signs of Colorectal Cancer?
In the early stages, colorectal cancer may not cause any symptoms. As tumours grow and spread, patients may experience symptoms including:
- Rectum not feeling completely empty after a bowel movement
- Blood in the stool
- Rectal bleeding
- Gastrointestinal discomfort such as gas, abdominal cramps, and feeling bloated
- Rectal pain or discomfort
- Mass in the abdomen or rectum
- Fatigue and weakness
- Nausea and vomiting
- Changes in appetite
- Unexplained weight loss
- Bowel obstruction
- Swollen lymph nodes
- Pain in the abdomen, back, buttocks, or legs
- Difficulty breathing
When Should Healthcare Providers Refer Patients for Colorectal Cancer Screenings?
The Canadian Cancer Society recommends that adults ages 50 to 74 and those not at high risk for colorectal cancer should have a stool test every two years. People at higher risk should discuss additional screening options with their doctors.
Patients showing symptoms of colorectal cancer should be referred for additional testing, including bloodwork, CT or MRI, and colonoscopy.
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