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.
Types of Colorectal Cancer
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.
Pre-Cancerous Colorectal Growths
Most bowel cancers start as benignnot cancerous, can grow but will not spread to other body parts 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 adenomaa benign tumour that develops from the epithelial lining of glands in the body (or adenomatous polyp) is a 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
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
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
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.
Hyperplastic Adenomas
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
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
Cancerous colorectal growths are often categorised by the types of cells the cancer originates from.
Adenocarcinomas
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 adenocarcinomacancer arising from mucus-producing glands in organs. While adenocarcinomas can be aggressive, they can have a good prognosisto predict how a disease/condition may progress and what the outcome might be if caught early.
Splenic Flexure Cancer
Splenic flexure cancer is a rare form of colon cancer that develops in the splenic flexure, a sharp bend that connects the transverse colon (middle portion of the colon) to the descending colon (left portion of the colon that leads to the rectum). It is often diagnosed in the later stages of disease, and can be associated with bowel obstruction. Because of how rare splenic flexure cancer is, there has been limited research done into the risk factors and treatment of this disease.
Rare forms of Colorectal Cancers
These forms of colorectal cancers are very rare:
- Colorectal lymphoma.
- Colorectal squamous cell carcinomas (cancer arising from squamous cells lining the GI tract).
- Colorectal neuroendocrine tumours.
- Gastrointestinal Stromal Tumours.
Treatment
If colorectal cancer is detected, it will be staged and graded based on size, metastasis, 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:
- T (tumour) indicates the size and depth of the tumour.
- N (node) indicates whether the cancer has spread to nearby lymph nodessmall bean-shaped structures that filters harmful substances from lymph fluid.
- M (metastasis) indicates whether the cancer has spread to other parts of the body.
This system can also be used in combination with a numerical value, from stage 0-IV:
- Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
- Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
- Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
- Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
- Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advancedat a late stage, far along or metastatic cancer.
Cancers can also be graded based on the rate of growth and how likely they are to spread:
- Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
- Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.
- Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.
Once your tumour has been staged and graded, your doctor may recommend genetic testinga procedure that analyses DNA to identify changes in genes, chromosomes and proteins, which can be used to analyse tumour DNA to help determine which treatment has the greatest chance of success, 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:
- Surgery, potentially including:
- Right or left hemicolectomyremoval of a portion of the colon; can be the right side (right hemicolectomy) or the left side (left hemicolectomy).
- Sigmoid colectomysurgery to remove the sigmoid colon.
- Colectomycomplete or partial removal of the colon.
- Proctocolectomysurgical removal of the colon and rectum.
- Chemotherapya cancer treatment that uses drugs to kill or slow the growth of cancer cells, while minimising damage to healthy cells.
- Clinical trialsresearch studies performed to test new treatments, tests or procedures and evaluate their effectiveness on various diseases.
- Palliative carea variety of practices and exercises used to provide pain relief and improve quality of life without curing the disease.
Treatment options for rectal cancer may include:
- Surgery, potentially including:
- High anterior resectionremoval of the lower left end of the colon and the upper portion of the rectum.
- Abdominoperineal resectionsurgical removal of the anus, rectum and a portion of the sigmoid colon through an incision in the abdomen.
- Ultra-low anterior resectionremoval of the lower left part of the colon and part or all of the rectum.
- Chemotherapy.
- Radiation therapya treatment that uses controlled doses of radiation to damage or kill cancer cells.
- Clinical trials.
- Palliative care.
Risk factors
While the cause of colorectal cancer remains unknown, the following factors may increase the likelihood of developing this disease:
- Being over 50 years old.
- Having colorectal polyps.
- Having certain diseases, such as Crohn’s disease or ulcerative colitis.
- Having a history of bowel, ovarian and/or endometrial cancer.
- Being obese.
- Having an unhealthy diet.
- Excess alcohol consumption.
- Having a history of smoking.
- Genetic mutations.
- Having a family history of bowel cancer.
- Having certain genetic conditions, potentially including:
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.
Symptoms
In the early stages of colorectal cancer, the disease may be asymptomatic. As the cancer progresses, some of the following symptoms may appear:
- Changes in bowel movements, potentially including:
- Diarrhoea.
- Constipation.
- Feeling of incomplete bowel movement.
- Thin bowel stools.
- Blood in stools.
- Rectal bleeding.
- Abdominal pain, bloating and/or cramping.
- Anal and/or rectal pain.
- A lump in the anus or rectum.
- Unexplained weight loss.
- Unexplained fatigue.
- Anaemiaa condition where there aren't enough red blood cells in the blood, causing fatigue, weakness and pale skin and affecting how the body responds to infection – potentially causing fatigue, weakness and/or weight loss.
- Changes in urinary habits, such as:
- Haematuriathe presence of blood in urine.
- Polyuriafrequent urination, especially at night.
- Changes in urine colour – becoming dark, rusty or brown colour.
Not everyone with the symptoms above will have cancer but see your general practitioner (GP) if you are concerned.
Diagnosis
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:
- Physical examinationan examination of your current symptoms, affected area(s) and overall medical history.
- Blood teststesting done to measure the levels of certain substances in the blood.
- Faecal occult blood test (FOBT)a test used to determine if there are microscopic traces of blood present in faeces or stool.
- Imaging tests, potentially including:
- MRI (magnetic resonance imaging)a type of medical imaging that uses radiowaves, a strong magnet and computer technology to create detailed images of the body.
- CT (computed tomography) scana type of medical imaging that uses x-rays and computer technology to create detailed images of the body.
- PET (positron emission tomography) scana type of medical imaging that uses radioactive tracers to create detailed images of the body.
- Barium studiesa type of x-ray where barium powder is either swallowed (barium swallow) or introduced via the colon (barium enema) to coat the organs of the digestive tract and provide clearer x-ray images.
- Colonoscopyan examination of the large intestine/bowel with a small, flexible instrument known as a colonoscope.
- Flexible sigmoidoscopyexamination of the lower portion of the large intestine and rectum with small, flexible instrument known as a sigmoidoscope .
- Biopsyremoval of a section of tissue to analyse for cancer cells.
