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Colorectal cancer is a cancer that starts in the cells that line either the colon or the rectum. These cancers can also be named colon cancer or rectal cancer respectively, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Colorectal cancer usually starts from a polyp, a growth that originates from the lining of the colon or rectum. Polyps are benign entities and can take 3-5 years to develop and an additional 2-3 years to turn cancerous. Finding and removing polyps can prevent colorectal cancer.
Most colorectal cancers are adenocarcinomas, which are cancers that begin in cells that line the inner colon or rectum. Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancerous and can spread to other areas of the body.
The colon is a 6-foot long muscular tube connecting the small intestine to the rectum. The colon–which along with the rectum is also known as the large intestine–is a highly specialized organ that is responsible for processing digestive waste so emptying the bowels is easy and convenient. The colon removes water from the stool (digestive waste matter) and stores the solid stool. Once or twice a day, it empties its contents into the rectum to begin the process of elimination.
The rectum is a 6-8-inch storage chamber that connects the colon to the anus. It is the rectum’s job to receive stool from the colon, to let you know there is stool to be evacuated, and to hold the stool until you are ready to evacuate that stool.
During digestion, food moves through the stomach and small intestine into the colon. The colon absorbs water and nutrients from the food and stores stool. Stool moves from the colon into the rectum before it leaves the body.
Cancer begins when normal cells begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
Depending upon the size, location and spread of the cancer, different modalities of therapy may be employed to treat the disease. It is important to fully understand the various treatment options available when managing the disease, whether the objective involves curative intent or promoting longevity and a good quality of life. The colon and rectum are made up of different layers of tissues. A polyp will start in the innermost layer (mucosa) of the colorectum and then grow toward the outer layers (one layer at a time).
If a tumour has grown through all layers of the colon or rectum, it may then spread to the nearby lymph nodes or tissue.
The large intestine is also known as the large bowel and commonly referred to as the colorectum or just the colon. The colon’s main function is to reabsorb large quantities of water and nutrients from undigested food products. If too much water is reabsorbed, constipation may result. Not absorbing enough water may result in diarrhea.
The rectum’s main function is to store feces, or waste material, before being expelled from the body. The colon itself is divided into different parts. It extends from the cecum to the anus and includes the following five component parts:
Each part of the colorectum serves a specific function in the elimination of waste. In the digestive process, the colon’s main functions are to:compact the chyme (liquefied food)absorb excess water from the chymereceive the B-vitamins that are produced by healthy intestinal bacteriamove compacted chyme and dead bacteria into the rectum and out of the body.
Not all colorectal cancers are hereditary, but all colorectal cancers are caused by genetic mutations.
Approximately 70-75% of colorectal cancers are sporadic: these are cancers that occur in people who do not have a family history of that cancer or an inherited change in their genetic material (DNA) that would increase their risk for that cancer.
All cancers are the result of gene mutations. The vast majority are sporadic occurrences with only some caused by hereditary genetic syndromes. Genetic conditions involve a largely unpredictable interplay of many factors and processes. Just because you hold a genetic mutation for something does not necessarily mean it will be expressed in your lifetime, but knowing your risk can save your life. Please read on to learn more about the genetics behind colorectal cancer.
To learn more about the role of genetics in colorectal cancer, check out our information booklet.
If a person has been diagnosed with colorectal cancer, one of the first things they will want to know is the stage of their cancer. The stage refers to the extent of the cancer or how far it has spread. The stage of colon or rectal cancer is important because it will determine the best therapeutic approach in the management of the disease.
The tool used to describe the stage of a patient’s disease is the TNM Staging System. Doctors use the results from diagnostic tests and scans to answer these questions:
Tumor (T): Has the tumor grown into the wall of the colon or rectum? If so, how many layers of the colorectal wall are affected?
Node (N): Has the tumour spread to the lymph nodes? If so, where and how many lymph nodes are involved?
Metastasis (M): Has the cancer spread to distant organs of the body? If so, where and how many organs are involved?
The results are combined to determine the stage of cancer for each person.
For colorectal cancer, staging often can’t be completed until after surgical resection of the primary tumour has taken place to remove the primary tumour along with surrounding tissue containing lymph nodes, and possibly lesions found on other organs.
There are five stages (Stage 0 through IV) to colorectal cancer. After each element has been determined, they are combined to form an overall stage of the cancer in roman numerals. The higher the roman numeral, the more advanced the cancer. This is generally how the cancer is referred to between doctor and patient:
As colorectal cancer progresses from Stage 0 to Stage IV, the cancer cells grow through the layers of the rectum wall and spread to lymph nodes and then to distant organs. The liver and lungs are the most common sites of spread in patients with colorectal cancer.
The size of the colorectal tumor does not appear to be important when it comes to outcomes. The aggressiveness of colorectal cancer is based entirely upon its ability to grow and invade the colorectal wall, lymphatic system, and blood vessels.
While some people start the journey due to routine recommended checkups (screening), others do so because of troubling symptoms, or an abnormal physical exam, or a new finding on a lab test such as iron deficiency anemia. Screening, such as FOBT and FIT, is intended for the “average risk Canadian” – a person who does not have symptoms from colorectal cancer and does not have a first degree relative who was diagnosed with colorectal cancer. It typically is recommended for people aged 50 and older, but the test cannot officially diagnose colorectal cancer. Instead, a diagnostic (rather than a screening) test is required such as a colonoscopy, biopsy, or imaging tests to confirm the diagnosis of colorectal cancer, as well as to define the extent of the disease.If a screening test such as FOBT or FIT has come back positive, your doctor will recommend that you undergo a diagnostic colonoscopy. Your doctor may also recommend such a test if symptoms or the results of a physical exam or blood tests suggest that colorectal cancer might be present.
Colorectal Cancer Resource & Action Network (CCRAN) has issued the following summary based on the latest Canadian Cancer Statistics issued by the Canadian Cancer Society, Statistics Canada, the Public Health Agency of Canada and the Provincial/Territorial Cancer Registries. We have presented colorectal cancer-relevant information but should you wish to view the publication concerning all statistics, it can be found here.
We don’t really know why colorectal cancer develops in some people and not in others. However, the same risk factors have been identified over the years which increase a person’s risk of developing colorectal cancer.
A risk factor is something that may increase a person’s chances of developing a disease or condition. Risk factors for colorectal cancer can be divided into two main groups: those that you cannot change and those that are lifestyle-related and, therefore, can be changed by you.
In the early stages of colorectal cancer, many people often do not experience any symptoms. This is why the disease is often referred to as “silent”.
When symptoms do appear, they will likely vary, depending on the cancer’s size and location in the large intestine–also known as the colorectum–which is comprised of the colon and the rectum. Symptoms of colorectal cancer may include:
Recent studies indicate that, on average, patients will typically be diagnosed approximately 14 weeks after the onset of their symptoms. There is no association between overall duration of symptoms and the stage of the tumor. Therefore, it is best to get regular screenings rather than rely on colorectal cancer symptoms to alert one to the presence of a tumor, as colorectal cancer can grow for years before causing any symptoms.
Colorectal cancer is the second leading cause of cancer death in Canada, but it is also a cancer that we may be able to prevent.
According to research, approximately 50% of cancer incidences are said to be preventable through the adoption of a healthy diet, physical activity, and weight management. Cancer prevention entails measures taken to lower the chance of getting cancer. To prevent new cancers from developing, scientists look at risk factors and protective factors.
Anything that increases your chance of developing cancer is called a cancer risk factor.
Conversely, anything that decreases your chance of developing cancer is called a cancer protective factor. Recommendations to help prevent colorectal cancer include:
Colorectal cancer is the third most diagnosed cancer in Canada. It is the second leading cause of death from cancer in Canadian men and the third leading cause of death from cancer in Canadian women. It is, however, the most preventable cancer through screening!
Screening means checking for a disease in a group of people who do not show any symptoms of the disease. Cancer screening tests help find colorectal cancer before any symptoms develop and signs of colorectal cancer are discovered by your doctor. When colorectal cancer is found and treated early, the chances of successful treatment are far better.
Colorectal cancer typically starts as a polyp – a benign growth in the lining of the colon or rectum. If left unremoved, these polyps grow in size and can also grow in number in the colon or rectum. In time (5-10 years), these polyps may become malignant (cancerous), capable of invading nearby tissue and distant organs, such as the liver or lungs. Screening for polyps or early-stage tumours will help ensure treatment is most effective before the disease spreads outside the colon or rectum and signs of colorectal cancer manifest.
Speak to your doctor to discuss your risk and determine the most appropriate screening plan for you. It could save your life.
