The colon and rectum make up the large intestine (or large bowel), which is part of the digestive system, also called the gastrointestinal (GI) system.

The colon is the longest part of the large intestine (the first 1.5-1.8 metres). It receives almost completely digested food from the caecum (a pouch within the abdominal cavity that is considered to be the beginning of the large intestine), absorbs water and nutrients, and passes waste (faeces) to the rectum.2

Most of the large intestine is made up of the colon, a muscular tube about 1.5-1.8 metres long.2

The rectum is the lowest 12-15cm of the large bowel, is relatively fixed in position behind the peritoneum (the tissue that lines the abdominal wall).

What is colorectal cancer

Most colorectal cancers start as a growth, called a polyp, on the inner lining of the colon or rectum.4

Over time (usually many years), some polyps can change into cancer. The chance of a polyp turning into cancer depends on the type of polyp.4 The different types of polyps are:4

• Adenomatous polyps (adenomas): these polyps sometimes change into cancer, and because of this, adenomas are called a pre-cancerous condition. There are three types of adenomas: tubular, villous, and tubulovillous.
• Hyperplastic polyps and inflammatory polyps: these polyps are more common, but in general they are not pre-cancerous. Some people with large (more than 1cm) hyperplastic polyps might need colorectal cancer screening with colonoscopy more often.
• Sessile serrated polyps (SSP) and traditional serrated adenomas (TSA): these polyps are often treated like adenomas because they have a higher risk of becoming cancerous.

When cancer forms in a polyp, it can grow into the wall of the colon or rectum. The walls of the colon and rectum are made up of multiple layers – the cancer starts in the innermost layer (the mucosa) and can grow outward through some or all the other layers.4

When cancer cells are in the wall, they can then grow into blood or lymph vessels. From there, they can travel to nearby lymph nodes or to other parts of the body.4

The stage (extent of spread) of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum.

Causes of colorectal cancer

Some factors that increase the risk of colorectal cancer include:1,3,4

• Inherited genetic risk and family history
• Inflammatory bowel disease such as Crohn’s
• High red meat consumption, especially processed meats
• Diet low in fibre
• Polyps
• Being overweight or obese
• High alcohol consumption (≥4 drinks/day)5
• Smoking
• Having a previous diagnosis of colorectal cancer
• Having other disease such as Type II diabetes

Symptoms of colorectal cancer

Symptoms of colorectal cancer include:1,3

• Change in bowel habit including diarrhoea, constipation or the feeling of incomplete emptying
• Change in appearance of consistency of bowel movements such as watery stools
• Blood in stools
• Abdominal pain, bloating or cramping
• Anal or rectal pain
• A lump in the anus or rectum
• Weight loss
• Unexplained fatigue
• Tiredness and/or anaemia (pale complexion, weakness, and breathlessness)

General side effects:7

• Soreness and swelling around the treatment area
• Tiredness and lethargy for a few weeks after you finish treatment.

Specific side effects (depending on the area being treated):

• Digestive issues – reduced appetite, pain, discomfort, or bloating
• Change in bowel habits
• Change in bladder habits
• Nausea or vomiting.

Most of these side effects will ease shortly after treatment is finished. Your team will discuss any long-term considerations with you depending on the tumour type.

Side effects8

Whether you experience side effects and how severe they are, depends on the type and dose of drugs you are given and your reaction from one treatment cycle to the next.

• Most side-effects are short-term and can be managed.
• They tend to gradually improve once treatment stops and the normal, healthy cells recover.

You may worry about the side effects of chemotherapy. If you feel upset or anxious about how long treatment is taking or the impact of side effects, let your doctor or nurse know.

• Get as much rest as possible
• Eat a wholefood, varied diet    
  • Appetite changes are common, and you may experience taste changes or nausea – help manage this by eating small, frequent snacks, avoiding smells that make you feel nauseous, eating foods that interest you rather than what you think you ‘should’ eat
• Keep up your water intake
• Reach out to support groups and others who have had
• Ask your team about topical treatments for skin if you are getting irritation or pain
• Stay out of the sun as much as possible throughout your treatment
• Record your side effects in a diary or journal
• Take some gentle exercise, such as walking, if you feel up to it. Light to moderate exercise can reduce treatment-related fatigue and improve mood.
  • It is important to acknowledge when you are fatigued, and rest when you need to. Plan your exercise for times in the day when you know you have more energy
• Ask for, and accept, help from family, friends and neighbours
• Be open with employers about your treatment and discuss flexible working options where need.

1. Cancer Council. Bowel cancer. Available at: cancer.org.au/cancer-information/types-of-cancer/bowel-cancer. Accessed on: 15/07/21.
2. Kahai P, et al. Anatomy, Abdomen and Pelvis, Large Intestine, 2020 StatPearls Pub, USA.
3. Cancer Council Australia. Clinical practice guidelines for the prevention, early detection and management of colorectal cancer. Available at: cancer.org.au/australia/Guidelines:Colorectal_cancer#_ga=2.99481630.1470258732.1626230418-908501624.1616558293. Accessed on: 15/07/21.
4. American Cancer Society. What is colorectal cancer? Available at: cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html. Accessed on: 15/07/21.
5. Fedirko V et al. Annals of Onc 2011; 22:1958-1972.
6. Li D, et al. Cancer Biol Med2014; 11(4):217-236.
7. Cancer Council Australia. Radiation therapy. Available at: https://www.cancer.org.au/cancer-information/treatment/radiation-therapy. Accessed on: 15/07/21.
8. Cancer Council Victoria. Chemotherapy side effects. Available at: https://www.cancervic.org.au/cancer-information/treatments/treatments-types/chemotherapy/side_effects_of_chemotherapy.html. Accessed on: 15/07/21.

Disclaimer
Any procedure including treatments involving radiation carry risks, including skin irritation and associated pain. Before proceeding with a referral for treatment, patients should be advised to seek a second opinion from an appropriately qualified health practitioner. As in any medical procedure, patient experiences and outcomes will vary.