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Colorectal cancer, also known as bowel cancer, is a malignancy that develops in any portion of the colon or rectum. Depending on where the cancer originates from, it may also be referred to as colon or rectal cancer.
The colon and rectum are towards the end of the body’s gastrointestinal (GI) tract, which is located in the abdomen. The lower GI tract is divided into three separate areas: the small bowel, the large bowel and the anus. The small bowel receives food from the stomach and absorbs the nutrients from the food. It is comprised of three separate parts (the duodenum, jejunum and ileum). The food is then passed onto the large bowel, where water and salts are absorbed. The large bowel also consists of three parts (the caecum, colon and rectum). What is left over is turned into solid waste (faeces or stool), and is sent to the anus to be removed from the body.
Colorectal cancers develop in the large bowel. However, cancers of the small bowel and anus can rarely occur. For more information on these cancers, please refer to the Rare Cancers Australia Knowledgebase.
Colorectal cancer is more common in males, and are generally diagnosed in people over 50. However, anyone can develop this disease.
Colorectal Cancers can be categorised based on the types of cells (such as cancerous or pre-cancerous), as well as the size, shape and type of cells affected.
Most bowel cancers start as benign growths – or polyps - on the wall or in the lining of the bowel. While polyps are usually harmless, they can become cancerous if they are of adenomatous origin. An adenoma (or adenomatous polyp) is a non-cancerous or benign tumour that can be considered a pre-cursor to cancer if it is not treated.
Adenomatous polyps are often classified by their shape and size.
Tubular adenomas are the most common subtype of bowel polyp, and generally a small, tube or spiral shaped tumour. They generally form over many years, and may become cancerous if left untreated.
Villous adenomas are generally larger and grow in a cauliflower shape with finger-like projections. These types of tumours are rare, and likely to become cancerous.
Tubulovillous adenomas generally contain a mixture of tubular and villous adenoma growths. They vary in size and growth patterns, and may become cancerous if left untreated.
Hyperplasia is defined as enlargement of an organ or structure due to excess cell production. These types of tumours are relatively common, and rarely become cancerous.
Inflammatory adenomas often occur in patients with an inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis. These types of growths rarely become cancerous.
Cancerous colorectal growths are often categorised by the types of cells the cancer originates from.
Adenocarcinomas are the most common type of colorectal cancer. These tumours originally begin as a benign adenoma formed from glandular cells, before developing into a malignant adenocarcinoma. While adenocarcinomas can be aggressive, they can have a good prognosis if caught early.
These forms of colorectal cancers are very rare:
If colorectal cancer is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.
Cancers can be staged using the TNM staging system:
This system can also be used in combination with a numerical value, from stage 0-IV:
Cancers can also be graded based on the rate of growth and how likely they are to spread:
Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment for colon and rectal cancers are treated differently, and often depend on several factors, including location, stage of disease and overall health.
Treatment options for colon cancer may include:
Treatment options for rectal cancer may include:
For more information on the treatment options, please refer to the Rare Cancers Australia Treatment Options page.
While the cause of colorectal cancer remains unknown, the following factors may increase the likelihood of developing this disease:
Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.
In the early stages of colorectal cancer, the disease may be asymptomatic. As the cancer progresses, some of the following symptoms may appear:
Not everyone with the symptoms above will have cancer but see your general practitioner (GP) if you are concerned.
If your doctor suspects you have a colorectal cancer, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they will examine your body (more specifically, around the abdomen) to check for any abnormalities. They may also perform a digital rectal examination (DRE), which is an exam conducted by a urologist (a doctor specializing in issues pertaining to the kidneys, bladder, prostate, and male reproductive system). In this exam, the doctor will insert a finger (or ‘digit’) into your rectum to feel the anus. If it feels hard or is an odd shape, further testing may be required.
Blood tests are used to assess overall health and detect any abnormalities. Some of these tests may include:
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), CT colonography and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis.
A colonoscopy is the main diagnostic test used for colorectal cancers. This procedure examines the lining of the entire large bowel, and can detect if any polyps or abnormal tissue are present. Your doctor will insert a long, flexible tube with a light attached (colonoscope) through your anus, rectum and colon while you are under an anaesthetic. Carbon dioxide or air may be pumped through the colonoscope for better visualisation of the bowel.
A flexible sigmoidoscopy is similar to a colonoscopy; however, this procedure only examines the rectum and lower portion of the colon. The instrument passed through the anus is shorter, and called a sigmoidoscope.
Once the location(s) of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. The tissue sample will then be analysed for cancer cells. This can be done by a fine needle aspiration (FNA) or a core needle biopsy (CNB).
While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, early-stage colorectal cancers have a better prognosis and survival rates. However, if the cancer is advanced and has spread, the prognosis may not be as good and there may be a higher risk of cancer recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.
Page last updated: 26/04/2023