Bowel cancer, also known as colon, rectal or colorectal cancer, occurs when abnormal cells grow uncontrollably…
- Cancer is the general name for a group of more than 100 diseases. Although there are many kinds of cancer, all cancers start because abnormal cells grow out of control.
- If cancers are detected early, treatment can often result in good outcomes.
- Certain cancers can be prevented by avoiding particular risk factors, such as cigarette smoke, or by participating in community screening programs, such as breast cancer screening using mammograms.
What is cancer?
Cancer is a broad term that describes a large number of conditions where abnormal cells grow uncontrollably in the body, invade and damage healthy tissues. Cancers are among the leading causes of death in Australia. For most types of cancer, early detection and treatment will improve the chances of overcoming the disease. A few types of cancer can be prevented by vaccination; for many others, avoiding risk factors is key.
Within every cell in our bodies are control mechanisms that regulate its growth, telling it when to multiply and when to stop multiplying. When the DNA of a healthy cell in a body changes (mutates) in such a way that these mechanisms are disrupted, the cell 'loses its brakes' and multiplies uncontrollably.
Any agent that can harm a cell's DNA is known as a carcinogen. Carcinogens can be physical (such as radiation), chemical (such as cigarette smoke), or biological (such as certain viruses). In many cases, the exact cause of DNA damage is unknown.
In every human body, DNA damage occurs on a regular basis. In the overwhelming majority of cases, the body's own protective mechanisms take care of the abnormal cell without us even noticing. However, on rare occasions an abnormal cell evades the body's defenses and creates a tumour - a mass of cells.
Tumours can be benign or malignant. Only malignant tumours are cancers.
Benign tumours (not cancerous)
A benign tumour will stay and grow at the original spot where it originated, and does not spread to other parts of the body. Benign tumours are not cancers, but some of them have the potential to become cancerous as they continue to grow, since the cells in the tumour can undergo further mutations, and acquire the ability to move to other parts of the body.
Benign tumours can also cause problems by pressing on neighbouring structures and organs.
Malignant tumours (cancerous)
Malignant tumours invade nearby tissues and spread throughout the body via the bloodstream or lymphatic system, and can continue to grow in these distant sites to form secondary cancers. This process is known as metastasis.
Cancers that are identified before they invade surrounding tissues have the best chance of a cure. Once a tumour has spread to other parts of the body, it becomes much more difficult to treat.
There many different cancer types, which are based upon the cell or organ of origin:
- Carcinomas originate in the cells that line the body cavities;
- Sarcomas originate in the cells of connective tissues such as muscles, bones and fat;
- Lymphomas originate in cells in the lymphatic system;
- Leukaemias and myelomas originate in bone marrow cells that produce white blood cells, and;
- Central nervous system cancers originate in the brain and the spinal cord.
Cancers are also defined by the extent the cancer has invaded beyond its original site, known as their stage. Factors used to define stages include:
- The size of the cancer;
- Whether the cancer is still restricted to its original site or has spread to nearby tissues;
- Whether the cancer has spread to lymph nodes, and if so, to how many and at what locations, and;
- Whether the cancer has spread throughout the body to distant organs.
There are different ways to stage different cancers. In general:
- Stage 0 - cancer in situ: the cancer cells are only on the surface of where the cancer starts. This is the best situation, since treatment starting at this stage almost always results in a cure.
- Stage 1 - localised cancer: cancer cells are found only in one location; the growth invades into the tissue.
- Stage 2, stage 3 - regional spread: cancer cells have spread to nearby tissues, including lymph nodes near the original site.
- Stage 4 - distant spread and metastasis: cancer cells have spread throughout the body and established themselves in multiple locations. At this stage, the cancer is generally more difficult to treat.
- Age - cells become less able to properly repair damage over time, which is partly why the risk of cancer increases with age;
- Lifestyle factors - smoking, alcohol overuse, a poor diet and a lack of physical activity all increase your risk of developing cancer;
- Genetics and family history - for some cancers, specific genes have been identified that put people who have these genes at a greater risk of developing cancer;
- Viruses and other pathogens - for example, hepatitis B and hepatitis C viruses, and human papillomavirus (HPV) can cause different cancers;
- Chemical exposure - some chemicals such as cigarette smoke and asbestos are highly carcinogenic;
- Radiation exposure - natural radiation such as ultraviolet (UV) rays from the sun, or man-made radiation from devices such as X-ray machines can increase your risk of cancer. Medical devices that release radiation are used when the benefits are thought to outweigh the risks, and;
- A weakened immune system - certain problems with your immune system (such as HIV/AIDS) can increase your risk of developing some types of cancer.
Methods for diagnosis
Individuals without symptoms (early detection)
Detecting cancer early results in the best outcomes. Since the early stages of cancer can often develop without causing any symptoms, population screening is needed to identify these people.
Population screening is a test offered to all people within a defined age, who may develop a certain type of cancer.
Screening tests are not 100% accurate and results can change as the body changes over time, which is why it is important to be screened at regular intervals.
Sometimes a cancer is detected by chance, such as during examinations carried out for other reasons.
If you are concerned that your symptoms may be suggestive of cancer, talk to your doctor even if the results of your screening test did not indicate cancer.
Individuals with symptoms
People with symptoms that raise suspicion for cancer are recommended more specific tests. These include:
A blood test can be used to identify markers, for certain cancers, such as bowel cancer. These markers by themselves are not sufficient to diagnose cancer, but they can help support the diagnosis. Blood tests can indicate the genetic risk of acquiring particular cancers, especially breast cancer.
The following scans are commonly used to determine if and how far cancer has spread:
- Computerised tomography (CT) scan uses X-rays to develop a 3D image of the body;
- A magnetic resonance imaging (MRI) scan is like a CT scan, but uses magnetism instead of X-rays;
- A positron emission tomography (PET) scan uses a radioactive substance injected into the body to selectively highlight cancer cells. When combined with a CT scan, it produces images to help assess the size, location and spread of a cancer, and;
- Bone scan, which is used to check the bones for any signs that cancer may have spread to them.
Special tests or procedures can be used to detect cancer depending on the type of cancer suspected. For example, mammograms are used to test for breast cancer, laparoscopy and endoscopy for stomach cancer, and ultrasound is used to investigate prostate cancer.
A biopsy is the main way to know for certain if abnormal-looking cells are cancerous. A biopsy is a sample of tissue taken from the suspected cancer and analysed to determine if the cells present are normal or not.
Biopsies may be taken in many ways, depending on the size, location and type of the cancer. For example, a skin cancer biopsy is a simple procedure done in the doctor's clinic, whereas taking biopsies from internal organs requires surgery or other invasive procedures.
Types of treatment
Depending on the type and stage of the cancer, different treatment options are available. More than one form of treatment may be required.
Surgery is often the first line of treatment for many cancers. The specific type of surgical procedure and potential complications differ based on the location and type of cancer, as well as numerous other factors such as health of the individual, previous treatments and potential spread of cancer. You should talk to your doctor about the specific procedure you may be undertaking.
Chemotherapy works by attacking cancer cells and stopping their reproduction. Various drugs are used, which can be given intravenously or orally. They are often given in cycles: a course of treatment will be followed by a rest period that helps to reduce the treatment side effects. Side effects differ between the different drugs used; however, common side effects are described under 'Potential complications' (see below).
In this type of therapy, radiation is used to deliberately damage cancer cells. Radiation can be focussed directly on the cancer to magnify its damaging effects while minimising damage to healthy surrounding tissues.
Radiation can be delivered from outside the body, which then needs to travel through the body to reach the cancer (known as external beam radiation). Alternatively, small radioactive beads can be implanted near or within the cancer (known as brachytherapy).
Immunotherapy, also known as biologic therapy, is used for some types of cancer. It uses medications that encourage the body's immune system to fight the cancer.
Hormone therapy is used for some types of cancer. It is used to lower the body's hormone levels, which can reduce the risk of the cancer coming back, or slow or stop the growth of the cancer.
Drugs that block the action of enzymes involved in cell growth, given orally, can be used to help stop the growth of a cancer.
Some people diagnosed with cancer seek out complementary and alternative therapies. None of these alternative therapies are known to cure cancer, but some can help people feel better when used together with conventional medical treatment. It is important to discuss any treatments with your doctor before starting them.
Combining different therapies
The different types of therapies can be given either before or after surgery:
Adjuvant therapy is therapy that is given after surgery, with the aim of preventing the cancer from returning. It can take the form of radiotherapy, chemotherapy, hormone therapy or a combination of these treatments.
Like adjuvant therapy, neoadjuvant therapy also takes the form of radiotherapy, chemotherapy and/or hormone therapy, but is provided before surgery. In the case of breast cancer, for example, neoadjuvant chemotherapy may be used to shrink the cancer before surgery.
Treatment side effects
Side effects from cancer treatment can include:
- Nausea, vomiting and fatigue can result from chemotherapy and radiotherapy. Remember that whether or not the treatment makes you feel sick is not an indication of how well the treatment is working;
- Altered bowel habits: constipation frequently occurs during chemotherapy, probably as a result of anti-nausea and some pain-relief medication. Radiotherapy may cause diarrhoea;
- Joint and muscle pain can occur after a treatment session and can last a few days;
- Some types of chemotherapy can cause temporary hair loss from the head and body. The hair may grow back after treatment has ended, and;
- Tingling in the hands and feet - some chemotherapeutic agents can affect the nerves. It is important to tell your doctor if you develop these symptoms.
Different types of cancer can have specific complications. For example, coughing fits and fluid in the chest are complications of lung cancer.
The prognosis of cancer varies by the type and stage of the cancer.
When looking at cancer statistics, which generally refer to 'five-year survival rates', it is important to remember that survival rates are only an indication based on patients who were previously treated. Constant advances in cancer treatment are continually improving the rates of cancer survival and cancer cure, so an individual's outcome is often difficult to predict accurately.
Unfortunately, most cancers do not have a vaccine. However, you can reduce your risk of developing cancer by not smoking, not drinking alcohol to excess, eating a healthy diet and avoiding exposure to dangerous chemicals and sunlight during peak UV radiation.