Colorectal cancer (also called bowel cancer) means cancer in the large bowel (the colon) or in the section at the end of the bowel just before the anus (the rectum). It starts in the inner lining of the bowel and typically begins as growths on the inside of the bowel (polyps), which can become cancerous and spread if they are not detected and removed.
Bowel cancer is the second most common cancer diagnosed in both men and women. Australia has one of the highest rates of bowel cancer in the world. Approximately 9% of cancer deaths in Australia are due to bowel cancer.
Bowel cancer is more common in people aged over 50 years than in younger adults. The chance of developing bowel cancer before age 85 is about one in 11 for men and one in 15 for women.
What increases a person’s risk of bowel cancer?[edit source]
The risk of bowel cancer is increased by smoking, eating a high amount of red meat (especially when cooked until blackened), eating a high amount of processed meats (e.g. smoked, cured, salted or preserved meats), drinking alcohol, and being overweight or obese. The risk is reduced by regular physical activity and eating plenty of foods that contain fibre.
Bowel cancer runs in some families due to changes in the building blocks of cells that are passed through families (inherited genetic mutations). Some of these cause specific conditions, such as Lynch syndrome, familial adenomatous polyposis (FAP), and attenuated FAP. Doctors use a system of three categories to work out an individual’s level of risk. A person’s risk category depends on how many close relatives have bowel cancer and their age at diagnosis. Someone with several close relatives with bowel cancer, especially if they were diagnosed at a young age, has much higher risk of bowel cancer than someone with no close relatives with bowel cancer.
How is bowel cancer diagnosed?[edit source]
Signs and symptoms of bowel cancer may include bleeding from the bowel, abdominal pain, changes in regular bowel habits to more frequent looser stools (poo) or constipation, weight loss, or a reduction in the number of blood cells that carry oxygen to body tissues (anaemia). These symptoms are not always caused by cancer and can also be linked to less serious health conditions.
Bowel cancer may also be detected before any symptoms develop. In the National Bowel Cancer Screening Program, most screen-detected cancers are asymptomatic.
Most people with signs and symptoms, which may reflect a bowel cancer, go to their general practitioner (GP) first. If a GP thinks a person’s symptoms or physical findings could be due to bowel cancer, they will usually arrange further investigation with referral to a gastroenterologist or colorectal surgeon.
The next step is to have a colonoscopy. During this procedure, the health professional is able to view the entire large bowel using a colonoscope to inspect the lining of the bowel. This guideline recommends that people with symptoms of bowel cancer should have a colonoscopy as soon as it can be arranged, but no more than 120 days from first seeing a doctor about those symptoms.
If a colonoscopy shows that a person could have bowel cancer, a piece of the abnormal-looking bowel (biopsy) will be taken to be tested by a pathologist. The person may also need to have imaging, such as abdominal scans, before deciding the best type of treatment for the bowel cancer. Sometimes the first sign of bowel cancer is sudden blockage of the bowel. When this happens, bowel cancer is diagnosed by x-ray or computed tomography (CT) scan and usually requires an emergency operation. After bowel cancer is diagnosed, doctors work out how far it has spread (cancer stage). This may be done by checking findings of the scans. Tissue taken at the time of colonoscopy may be tested for genetic changes in the cancer cells, which can help determine the best treatment. The health professionals treating the person will work closely together to get an accurate understanding of the cancer.
There are several different systems for recording cancer stage. All these systems use codes based on letters and numbers, to indicate how far the cancer has spread through different tissues and organs, and how much cancer is still in the body after surgery. Australian doctors use a combination of these staging systems. Being diagnosed with bowel cancer can be stressful and frightening. Supportive care to help cope with these feelings is an important part of treatment for bowel cancer. Doctors should check whether people are distressed and provide psychological support, if needed. This may include referral to a health professional or organisation such as Cancer Council.
How can we reduce bowel cancer in Australia?[edit source]
Testing healthy people for early signs of bowel cancer (screening) can reduce the number of deaths due to bowel cancer. Australia has a National Bowel Cancer Screening Program, which involves mailing faecal occult blood test (FOBT) kits to people in the target age groups. The person collects tiny samples of their stools (poo) at home and sends them to a testing centre, where the sample is examined for invisible traces of blood. If the test finds some blood (i.e. the result of the test is positive), the person is advised to have more tests, in particular, colonoscopy. In Australia, the screening strategy with the best balance of effectiveness, avoiding unnecessary tests, safety and value for money, is to offer a FOBT every 2 years to people aged 50–74, provided they do not have symptoms of bowel cancer or are not from a high-risk family.
There are a lot of studies indicating that regular aspirin taken by people older than 50 years can reduce the risk of developing bowel cancer. Although there are some risks of taking aspirin, everyone should consider taking a low dose (e.g. 100 mg) of aspirin every day for at least 2.5 years, starting between the ages of 50 and 70 years, unless there are reasons not to such as previous ulcer symptoms. People genetically at risk for bowel cancer or with a strong family history of bowel cancer should particularly consider taking aspirin. Individuals should talk to their GP about whether it would be suitable for them to take aspirin to prevent bowel cancer.
People from high-risk families need extra screening tests to find bowel cancer early. This includes having a colonoscopy every 5 years or more frequently in some circumstances. The age at which a person should start regular bowel screening tests depends on their risk category. They may also be advised to start taking low-dose aspirin regularly from age 25.
How is bowel cancer treated?[edit source]
Treatments for bowel cancer include surgery, chemotherapy and radiation treatment.
Most people with bowel cancer have an operation to remove as much of the cancer as possible. This may happen straight after getting the diagnosis, or after having chemotherapy and/or radiation treatment for a few months first (for example, if the cancer is in the rectum). Whether an operation is best for the person, and the type of operation, depends on the size of the cancer and how far it has spread, their general health, and their personal choice.
Surgery can either be a traditional operation through a long incision in the abdomen, or by ‘keyhole surgery’ (laparoscopy). Laparoscopy should only be done in hospitals with special expertise in this technique and by surgeons with the right training and skill.
Before the operation, the person will have a medical assessment, including blood tests, so that any problems such as anaemia, iron deficiency or malnutrition can be treated before the operation. Blood clots in people having surgery for bowel cancer should be prevented by using compression stockings, machines to keep the blood flowing to the legs (sequential compression devices), and blood-thinners such as low molecular-weight heparin. These preventive measures may need to be continued for 4 weeks after surgery.
Infections in the surgical wound are common after bowel cancer surgery. Some surgeons try to reduce the risk of infection by using laxatives to empty the bowel before surgery (mechanical bowel preparation).
Sometimes the low part of the bowel close to the anus needs to be removed, but this is uncommon. If this is necessary, the person can no longer pass bowel motions (stool, poo) through their rectum and anus. When this happens, the surgeon makes a new opening (stoma) in the abdominal wall, which can be attached to a colostomy bag to collect faeces, instead of going to the toilet the normal way. Anyone who needs (or might need) a stoma should see a stomal therapist before their operation, and should be given education and support afterwards to take care of their stoma.
Chemotherapy and radiation treatment[edit source]
Chemotherapy uses drugs to kill cancer cells in the body. There are many different chemotherapy drugs and several different standard combinations. The best combination for a person with bowel cancer depends on how far the cancer has spread, the type of cancer, their age, and their general health. The oncologist and pathologist will look at the genetic mutations in the cancer to decide which chemotherapy drugs will work best. Radiation uses x-rays to kill cancer cells and is a common treatment for rectal cancer. Whether or not it is suitable for someone with bowel cancer depends on how far the cancer has spread, as well as other factors. If radiation is used, it is usually done before surgery.
When chemotherapy or radiation treatment is given before surgery for rectal cancer, the aim is to reduce the size of the cancer before it is operated on and minimse the risk of leaving any microscopic cells behind. This is called neoadjuvant therapy. In some cases the cancer may completely respond to this treatment. This is not common and can never be confirmed without surgery and examination of the specimen that has been removed. When chemotherapy and/or radiation treatment is given after surgery, it is called adjuvant treatment.
Chemotherapy after surgery is the standard treatment for people with colon cancer that has spread beyond the bowel, especially where it has spread to the lymph nodes but has not spread further. For people with colon cancer that has not spread to the lymph nodes, chemotherapy after surgery has not been proven to improve outlook, but there may be specific groups of people who this could help.
For people with rectal cancer, both chemotherapy and radiation are common treatments. Chemotherapy is often given alongside radiation treatment to boost the effect of the radiation, and both treatments are given together over a course of several weeks. The combination of chemotherapy and radiation (chemoradiation) is recommended before surgery for most people with rectal cancer, to reduce the risk of the cancer returning. Surgery should be planned for 6–12 weeks after chemoradiation. Radiation treatment might be given on its own if the person is too unwell to cope with the combination of chemotherapy and radiation, or for people having shorter radiation treatment (‘short-course’ radiation).
Chemotherapy after surgery for rectal cancer aims to kill any remaining cancer cells that are invisible to the surgeon but could spread afterwards. However, the benefits are not as well proven for rectal cancer. For people with rectal cancer, their team of health professionals will assess various factors before recommending a treatment plan. Chemoradiation after surgery should be considered if a person has a high risk of rectal cancer returning and they did not have chemoradiation before their surgery.
Follow-up after surgery[edit source]
After surgery for bowel cancer, there is a chance that the cancer could come back (recurrence) due to microscopic cells undetectable to the surgeon and radiologist. The chance of recurrence depends on how advanced the cancer is and if the cancer was removed completely at surgery. As treatment for cancer gets better and better, recurrence rates are getting lower.
Recurring bowel cancer may or may not cause symptoms. The purpose of follow-up after surgery is to find new or regrowing cancer early so they can be treated. Check-ups should be done at regular intervals for 5 years after surgery. Surgeons, gastroenterologists, GPs and nurses can work together to provide thorough check-ups. Tests may include physical examination, regular colonoscopy, CT scans, and blood tests, including measuring the amount of carcinoembryonic antigen (CEA), which can indicate that there is a cancer.
What happens if bowel cancer returns or spreads?[edit source]
If cancer comes back after surgery, it can be confined to the bowel or bowel area, or it could be discovered after it has already spread (metastasised) in the blood or lymph vessels. The liver and lungs are the most common places to find these bowel cancer growths (metastases).
If the results of a person’s routine check-ups make their doctor suspect the bowel cancer has returned, more tests will be done. These tests could include another CEA blood test, CT scan of the chest, abdomen and pelvis, and positron emission tomography (PET scan). Other tests, such as magnetic resonance imaging (MRI scans), may also be needed.
If rectal cancer returns and is confined to the area around the rectum, the person will have the best chance of long-term survival if they have surgery to completely remove the cancer (pelvic exenteration), at a hospital that has the skills to do this operation. Chemoradiation before surgery should also be considered if not given previously. The risks and benefits should be carefully explained to the person before choosing surgery. If bowel cancer has spread to the liver or lungs, there is still a chance that it could be treated. Liver surgery to remove as much cancer as possible is the best option to improve the person’s chance of survival if there is cancer in the liver. If possible, chemotherapy may be given after liver surgery. If surgery is not possible because the cancer has spread too far in the liver, other treatments are available to destroy colon cancer cells in the liver. These include using radiation inside the liver, using chemotherapy and blocking blood vessels in the liver, using heat to kill cancer cells, injecting chemotherapy drugs into the liver artery, and special radiation treatment techniques. These techniques may be offered in some hospitals.
For people with bowel cancer that is not curable by surgery, treatment aims to prolong life and improve or maintain quality of life. Treatment can include surgery to prevent other problems like bleeding and blockage of the bowel, chemotherapy, radiation treatment, or a combination of these. Many different medicines and chemotherapy combinations are used to treat people with bowel cancer that has spread throughout the body (metastatic bowel cancer). The timing and combinations of drugs will vary between individuals, based on the patient and the results of pathology tests and genetic tests. Doctors should always discuss the side effects and the likely results of various treatments with the patient.