What is cancer?

Cancer is an uncontrolled, excessive growth of a cell mass (tumour) somewhere in the body. The body contains many trillions of cells. Some, like hair, skin and blood cells, multiply relatively quickly. Others, like brain cells, hardly replicate at all. The regulation of this rate in different tissues is very complex and involves many factors - some of which promote cell proliferation and some that slow it. In cancer, the balance between these opposing systems is disturbed in a manner that allows uncontrolled growth.

Unregulated cell division is dangerous, as the resultant tumour can squash or invade into nearby healthy tissue and stop it from functioning normally. Highly advanced cancers can break free and invade faraway tissues as well (metastasis).

Cancer is not a single disease, and may exist in many diverse forms. Cancers can arise from almost any of the many different tissues in the body. The most common types are skin cancer, prostate cancer, breast cancer, lung cancer and colon cancer. Each type is has different symptoms, behaviour, treatment and outcomes.

How does it happen?

On a daily basis, a few cells in our bodies accidentally acquire mutations in their DNA, but these are almost always repaired, or the offending cell destroyed by the immune system. Mutations can have enormously different effects on a cell, or no effect at all, depending on the gene affected. Certain mutations will cause a cell to multiply in excess (there are many different specific mutations that can have this effect).

Generally, a cell must accumulate several mutations before it has the potential to become cancerous. Occasionally, a cell will acquire enough mutations to escape the body's immune surveillance system, and go on to produce a tumour. People with weak immune systems, or those who have been exposed to mutation-inducing substances (cigarette smoke, UV radiation, asbestos, certain drugs and infections) are therefore at higher risk of getting cancer.

How bad is it?

There is no single answer to this. Every case of cancer is different, and the prognosis varies enormously - from 'almost certainly curable', to 'likely to cause death quickly'. It is impossible for anyone to give an exact life expectancy or guarantee a cure. Oncologists can give a good estimate of the likely course of disease - the chance of cure, likelihood of cancer coming back, and in some cases, the expected length of survival.

This is always an educated guess based on previous research, and many factors:

  • The patient: their age and general health, and whether they are well enough to undergo treatment.

  • The cancer: different types of cancer have different typical behaviours. Lung cancer, for example, tends to progress more quickly than prostate cancer. Furthermore, different subtypes of cancer within a certain cancer type may behave differently. The stage that a cancer has reached (how far it has spread) before it is diagnosed has a huge effect on the likelihood of cure and the estimated life expectancy.

  • The treatment: different treatments have different results. An oncologist is responsible for determining which treatment is most likely to produce the best effects for an individual.

The approach to cancer therapy and goals of treatment vary case by case. A radical approach aims to cure disease where possible, while a palliative approach is taken when disease is incurable. The latter does not mean that all hope has been given up - palliative treatment includes the goals of reduction in cancer mass and growth, improvement of symptoms and prolongation of quality life.

Treatment methods include: 

Surgery, performed by Surgeons

Radiotherapy, administered by Radiation Oncologists

Systemic drug therapies, medication prescribed by Medical Oncologists which includes:

  • Chemotherapy

  • Targeted therapy

  • Immunotherapy


Surgery and radiotherapy are often used to remove or destroy individual tumour masses in the hope of cure.  They are also used to relieve symptoms caused by  specific tumor masses in cases that are not curable.  They are both used to specifically treat localised areas of disease. 


Systemic drug therapies on the other hand, are whole-body (systemic) treatments targeting all cancerous cells in the body. They are used to treat cancers that are widespread, with multiple tumour deposits, too numerous to be completely removed by surgery or killed by radiotherapy. Chemotherapy is also often used in addition to primary treatment with surgery and/ or radiotherapy adding to their effectiveness and the chance of cure. 


Chemotherapy drugs traditionally target cells that are rapidly multiplying. Healthy cells with high turnover rates, like hair, bone marrow and gut cells, are therefore also at risk, giving rise to common side effects of chemotherapy like hair loss, nausea and bone marrow suppression. There are hundreds of different chemotherapy agents available, and each cancer has a different profile of susceptibility. Often, several chemotherapy agents are used in combination, given periodically in cycles which have effects lasting a few weeks at a time. Administration is most often through injection but can sometimes be given in tablet form.  Modern chemotherapy research is focusing on developing medications that are more specific to cancer cells and less toxic to healthy cells.


Targeted therapy also aims to kill tumor cells but its mechanism of action varies from chemotherapy in that it only targets cells with a particular mutation or excessive production of a growth factor produced primarily in cancer cells.  By targeting these growth pathways and inhibiting the proliferation of abnormal cells they also have the goal of decreasing the overall burden of tumor within the body.


The most recent class of drugs we use to fight cancer are known as immunotherapy agents.  By allowing our immune cells to more easily recognise abnormal cells in the body we can now fight cancer through our own defense mechanisms which many types of cancer previously were able to evade.  Some of these drugs are still in development and their effectiveness in some cancer subtypes is still being tested. In the case of metastatic melanoma however, they are now considered a first line treatment option as we now have good evidence of their effectiveness in this tumor subtype.   

How can we treat cancer? 

The spread of cancer to distant parts of the body through the bloodstream or lymphatic system. Metastatic cancers are high-grade, advanced cancers. Common sites of metastasis vary between cancer types.

A doctor specialising in cancer. Medical oncologists treat of cancer through medications (chemotherapy and other targeted medications), while Radiation oncologists use radiotherapy to treat cancer.

Cancer treatment with medicines. While surgery or radiotherapy are used to remove or kill the cells forming localised tumours originating at a particular site, chemotherapy acts throughout the body, either attacking smaller, microscopic deposits aiming  to "mop up" those too small to be detected by scans or aiming to attack lesions too numerous to be removed surgically. There are hundreds of chemotherapy drugs available. They are often used in combination, administered generally by injection but sometimes as tablets. 

Targeted Therapy
The use of drugs to target specific mutations in cancer cells causing uncontrolled cell replication and growth.  Different types of cancer have different specific mutations hence use of different targeted therapies in different cancer types.

Hormone therapy
A type of targeted therapy aimed at decreasing hormone levels which would otherwise stimulate the growth of cancer cells.  The two types of cancer sensitive to this type of treatment are breast cancer (where we aim to reduce the amount or decrease the effects of estrogen) and prostate cancer (where we aim to reduce the effects of testosterone) .

Drugs that help use the bodys own natural defenses to attack cancer cells.  By preventing the signals cancer cells develop to hide from the immune system and switching them on again our own immune systems may more effectively attempt to kill any abnormal cells.  Different types of cancer are more or less prone to the effects of immunotherapy.

The use of targeted radiation to destroy tumours in the body. Radiotherapy may be used in conjunction with surgery or chemotherapy. It may also be used instead of surgery for patients too ill to be surgical candidates.

Adjuvant therapy
A treatment (usually chemotherapy) used as an addition to a major primary treatment (usually surgery). Adjuvant treatment is not, in itself, curative, but increases the chance of cure from the primary treatment, and reduces the risk of cancer coming back. Adjuvant treatment is given after the primary treatment.

Neoadjuvant therapy
Similarly to adjuvant treatment, neoadjuvant treatment is used in addition to a primary treatment (usually surgery), in order to increase the effectiveness of that treatment. However, neoadjuvant treatment is given before surgery. The aim is to shrink down the tumour so that surgery has a higher likelihood of success. For example, neoadjuvant treatment may shrink a tumour down so that it is no longer close to vital structures that surgeons wish to avoid.

Palliative care is aimed at improving quality of life in incurable disease. It may involve chemotherapy to prolong life, palliative radiotherapy or surgery to shrink tumours causing troublesome symptoms, counselling, and treatment of symptoms like nausea and pain.

Staging is a classification system to describe how advanced a cancer is. Each cancer has its own staging system and specific criteria. Generally, cancers are staged from I (early disease, higher chance of cure) to IV (advanced disease, lower chance of cure). A cancer's stage is calculated based on its size, invasion of surrounding structures and extend of spread throughout the rest of the body. Cancer staging generally involves imaging scans. Re-staging is often performed during and after treatment to determine its effect.


Glossary of Cancer Terms