What is colorectal cancer?

Symptoms

• The symptoms of colorectal cancer vary with the location and size of the cancer.
• They may be similar to symptoms of more common, non-cancerous bowel conditions.
• Common symptoms include:
  • passing of blood, seen as red or black flecks on/in the stools
  • persistent change in bowel habits, alternating between diarrhoea, constipation and looser stools
  • sensation of being unable to empty your bowels, despite passing stools
  • unexplained weight loss
  • pale skin and tiredness due to lack of red blood cells or haemoglobin (anaemia) as a result of bleeding.

Diagnosis

• A doctor will take a thorough history and carry out a physical examination.
• Diagnosis of colorectal cancer is confirmed by a colonoscopy which enables the doctor to look at the whole colon and take small samples (biopsies) of any suspected tumours if necessary.

Representation of a colonoscopy examination to identify tumours.
Image credit: Shutterstock.

Types and incidence

• Each year 35,000 cases of colorectal cancer are diagnosed in the UK.
• Colorectal cancer is divided into three types:
  • hereditary
  • familial
  • sporadic.

Hereditary colorectal cancer

• This is where a known cancer-causing mutation has been passed down from generation to generation.
• About five to 10 per cent of people who develop colorectal cancer have inherited genetic mutations that cause the disease.
• The most common hereditary colorectal cancers are familial adenomatous polyposis and hereditary non-polyposis colorectal cancer.
• Individuals with these types are more likely to develop colorectal cancer at a younger age than those who do not have them.
• Familial adenomatous polyposis (one per cent of all colorectal cancers) is caused by an inherited mutation in the adenomatous polyposis coli (APC) gene, which is normally involved in regulating cell growth.
• Hereditary non-polyposis colorectal cancer (two to five per cent of all colorectal cancers) is caused by a mutation in one of the DNA repair genes involved in correcting mistakes made during DNA replication.

Familial colorectal cancer

• Parents with two or more first-degree (brothers and sisters) or second-degree (grandparents) relatives with colorectal cancer are considered to be at higher risk of the disease.
• Familial colorectal cancer is thought to be due to changes in an individual’s DNA that increase their susceptibility to the disease.

Sporadic colorectal cancer

• In most people who do not have a family history of the disease, several mutations are required for colorectal cancer to develop.
• It may take several decades for these mutations to accumulate, which is why 95 per cent of colorectal cancer cases occur in people over the age of 50, and 73 per cent occur in people over 65.
• Mutations in the APC gene are seen in 70 to 80 per cent of sporadic tumours.
• Mutations in DNA repair genes are seen in around 15 per cent of cases.

Causes and prevention

• Many different genetic and environmental factors have been linked to colorectal cancer.
• People with a history of adenomatous polyps or chronic bowel inflammation have an increased risk of developing colorectal cancer.
• A previous episode of colorectal cancer also increases the likelihood of the cancer reoccurring.
• Smokers have a higher risk of developing colorectal cancer than non-smokers.
• Diets high in fat and/or red meat increase an individual’s risk of colorectal cancer.
• Diets high in fibre and folate (found in vegetables) may reduce an individual’s risk but this could just be due to leading a ‘healthier’ lifestyle in general.
• Successful treatment of colorectal cancer and survival is more likely if the disease is discovered and treated early.
• Taking note of any changes in bowel movements could help identify colorectal cancer early.

Treatment

• Treatment depends on the location, size and spread of cancer, as well as the patient’s health and personal choice.
• Early stage colorectal cancer can be treated effectively with a surgical procedure called local resection. This involves removing the cancer from the bowel lining as well as a border of healthy tissue from around the cancer.
• Keyhole surgery may also be used to remove early stage tumours in a procedure called a laparoscopic resection.
• In more advanced cases, surgery may involve removal of a section of the colon containing the tumour. This procedure is called a colectomy.
• Combined chemotherapy and radiotherapy is sometimes used before surgery to shrink the tumour and make it easier to remove. Chemotherapy may be used after surgery to kill any remaining cancer cells.
• For incurable cases of colorectal cancer, surgery may be used to relieve symptoms such as vomiting resulting from bowel obstruction.
• New therapies are currently being developed to help target the cancerous cells more specifically and increase the survival rate of colorectal cancer patients.