Colorectal cancer is one of the most common and serious cancers affecting Canadians today. It develops in the large intestine — either in the colon or the rectum — and is the second leading cause of cancer death in Canada. The good news is that when caught early, colorectal cancer is highly treatable and sometimes curable. Understanding the symptoms, causes, and risk factors can help you take action sooner.
What Is Colorectal Cancer?
Cancer develops when cells grow abnormally and form a mass called a tumour. In colorectal cancer, these abnormal cells grow in the walls of the colon or rectum, which are the final parts of the digestive system.
Doctors often use the term “colorectal cancer” to cover both colon cancer and rectal cancer. This is because both types share very similar symptoms and treatments. For example, changes in bowel habits, bleeding, and abdominal pain can appear in either type.
According to Health Canada, colorectal cancer is the second most commonly diagnosed cancer in Canada. It is most common in people over the age of 50, though it can affect younger adults as well.
What Causes Colorectal Cancer?
Doctors do not yet know the exact cause of colorectal cancer. However, most cases begin with small growths in the lining of the colon or rectum called polyps.
Polyps are small, mushroom-shaped growths attached to the inner wall of the bowel. Most polyps are harmless (benign) at first. However, over time, some polyps can undergo changes and become cancerous.
How Polyps Become Cancer
The transformation from a polyp to a cancerous tumour is usually slow. It can take several years. This slow growth is actually helpful — it gives doctors a window of opportunity to find and remove polyps before they turn into cancer.
If a routine screening exam finds polyps early, a doctor can remove them surgically. This simple step can prevent colorectal cancer from developing in the first place. Therefore, regular screening is one of the most powerful tools we have against this disease.
Risk Factors for Colorectal Cancer
Certain factors can raise your chances of developing colorectal cancer. Some you can control, and some you cannot.
Age: Risk increases significantly after age 50.
Family history: Having a parent or sibling with colorectal cancer raises your risk.
A history of polyps: If you have had polyps before, you are more likely to develop them again.
Inflammatory bowel disease: Conditions like Crohn’s disease or ulcerative colitis increase risk over time.
Low-fibre diet: A diet high in red and processed meat and low in fibre is linked to higher risk.
Physical inactivity: A sedentary lifestyle is associated with greater colorectal cancer risk.
Smoking and heavy alcohol use: Both are known risk factors for many cancers, including colorectal cancer.
Obesity: Being significantly overweight increases risk, especially in men.
Furthermore, certain inherited gene mutations — such as Lynch syndrome or familial adenomatous polyposis (FAP) — greatly increase the risk of developing colorectal cancer. If your family has a history of these conditions, speak with your family doctor about genetic counselling.
Symptoms of Colorectal Cancer
One of the most dangerous aspects of colorectal cancer is that it often causes no symptoms in its early stages. By the time symptoms appear, the cancer may already be more advanced. This is why screening is so important even when you feel well.
Common Symptoms to Watch For
When symptoms do appear, they may include:
Blood in your stool or very dark, tarry stools
A change in bowel habits lasting more than a few weeks (such as diarrhea, constipation, or narrow stools)
A feeling that your bowel does not empty completely
Cramping or ongoing abdominal pain
Unexplained fatigue or weakness
Unintentional weight loss over several months
It is important to note that these symptoms do not always mean cancer. However, they should never be ignored.
How Symptoms Vary by Location
Symptoms can differ depending on where the tumour is located in the bowel.
Tumours on the right side of the colon (the ascending colon and cecum) often cause bleeding and anaemia — which may show up as unexplained fatigue and weakness. The stool may look normal despite the bleeding.
Tumours in the middle section (the transverse colon) are more likely to cause cramping and abdominal pain. Tumours on the left side or in the rectum often cause narrow, pencil-thin stools and visible blood streaks in the stool.
Conditions That Can Mimic Colorectal Cancer
Several other conditions share similar symptoms. These include:
Irritable bowel syndrome (IBS): A common digestive condition causing cramping, bloating, and alternating diarrhea and constipation.
Diverticulitis: Inflammation of small pouches in the bowel wall, causing abdominal pain.
Inflammatory bowel disease: Conditions like Crohn’s disease and ulcerative colitis cause inflammation of the bowel lining.
Hemorrhoids: Swollen blood vessels in the rectum that can bleed, sometimes confused with rectal bleeding from cancer.
Gastrointestinal infections: Bacterial infections like salmonella cause diarrhea and stomach pain.
Rectal ulcers: Sores in the rectum lining that can cause bleeding.
As a result, it is always best to have a doctor evaluate any persistent digestive symptoms rather than assuming they are caused by a minor condition.
How Colorectal Cancer Spreads
Colorectal cancer usually grows slowly. In many cases, it takes years for a tumour to grow large enough to cause symptoms. However, if it goes undetected and untreated, the cancer can spread beyond the bowel wall.
First, the cancer may invade nearby lymph nodes. From there, it can travel through the lymphatic system or bloodstream to other organs. The liver is the most common site for colorectal cancer to spread. It can also spread to the lungs, ovaries, and bones.
The outlook for colorectal cancer depends largely on how early it is caught. Early-stage cancer that has not spread beyond the bowel wall has a much better prognosis than cancer that has spread to other organs. This is another strong reason why regular screening saves lives.
You can learn more about how colorectal cancer develops from the Mayo Clinic’s colorectal cancer resource.
Colorectal Cancer Screening in Canada
Screening means testing for cancer before symptoms appear. In Canada, most provincial health plans cover colorectal cancer screening for eligible adults, typically starting at age 50.
The most common screening method is the fecal immunochemical test (FIT). This is a simple test done at home that checks your stool for hidden blood. If the FIT result is abnormal, your doctor will likely refer you for a colonoscopy — a procedure where a doctor looks inside the colon using a small camera.
A colonoscopy can find polyps and remove them during the same appointment. It is both a screening and a preventive procedure. Talk to your family doctor about when you should start screening based on your personal and family health history.
The World Health Organization’s colorectal cancer fact sheet also highlights how screening programmes dramatically reduce deaths from this disease worldwide.
When to See a Doctor
Do not wait for symptoms to get worse before reaching out for help. Book an appointment with your family doctor if you notice any of the following:
Blood in your stool or bleeding from the rectum
A significant change in your bowel habits lasting more than two to three weeks
Ongoing abdominal pain or cramping with no clear cause
Unexplained fatigue or weight loss
You are 50 or older and have not had a recent bowel cancer screening
If you do not have a family doctor, a walk-in clinic can be a good starting point. A clinic doctor can order basic tests, refer you for screening, or direct you to a specialist if needed. Many provinces also have cancer screening programme hotlines you can call for guidance.
Remember, early detection makes a real difference. A conversation with your doctor today could save your life tomorrow. This article is for information only — please always consult a qualified healthcare provider for medical advice specific to your situation.
Frequently Asked Questions About Colorectal Cancer
What are the early warning signs of colorectal cancer?
Early-stage colorectal cancer often causes no symptoms at all. However, some early signs may include blood in the stool, a change in bowel habits, or mild abdominal cramping. Because these symptoms can be subtle, regular screening is the most reliable way to catch colorectal cancer early.
At what age should Canadians start screening for colorectal cancer?
Most Canadian provinces recommend starting colorectal cancer screening at age 50 for people at average risk. If you have a family history of colorectal cancer or polyps, your doctor may recommend starting earlier. Talk to your family doctor about the right time to begin screening based on your personal health history.
Is colorectal cancer hereditary?
Yes, family history plays an important role in colorectal cancer risk. Having a parent, sibling, or child with colorectal cancer roughly doubles your risk. Certain inherited conditions, such as Lynch syndrome, increase the risk even further and may require earlier and more frequent screening.
Can colorectal cancer be cured?
When diagnosed at an early stage, colorectal cancer can often be treated successfully and, in many cases, cured. The five-year survival rate drops significantly when cancer has spread to other organs. This is why early detection through regular screening is so critical for improving outcomes.
What is the difference between colon cancer and rectal cancer?
Both are types of colorectal cancer, but they occur in different parts of the large intestine. Colon cancer develops in the long, upper portion of the large bowel, while rectal cancer forms in the last several centimetres before the rectum exits the body. They share many symptoms and risk factors, which is why they are often discussed together.
Does a high-fibre diet help prevent colorectal cancer?
Research suggests that a diet high in fibre — from vegetables, fruits, and whole grains — may help lower the risk of colorectal cancer. At the same time, reducing red and processed meat intake is also recommended. A healthy diet, combined with regular physical activity, supports overall bowel health and may reduce cancer risk.
Key Takeaways
Colorectal cancer develops in the colon or rectum and is Canada’s second deadliest cancer.
Most cases begin as small, non-cancerous polyps that slowly become cancerous over time.
Early-stage colorectal cancer often has no symptoms — screening is the best way to catch it early.
Common symptoms include blood in the stool, changes in bowel habits, fatigue, and abdominal pain.
Most Canadian provincial health plans cover colorectal cancer screening starting at age 50.
Removing polyps during a colonoscopy can prevent cancer from developing.
If caught early, colorectal cancer is highly treatable and often curable.
Speak with your family doctor or visit a walk-in clinic if you have any concerns about your bowel health.
