What is cancer?

Cancer is a significant health problem.1 In Australia, more than 130,000 new cancers are diagnosed every year, and one in two people will develop cancer before their 85th birthday.2

Although treatment advances mean more cancer patients can survive the condition, cancer remains a leading cause of death around the world.1 In New Zealand, cancer kills more people than any other disease.3 Having cancer and undergoing cancer treatment significantly impacts on the quality of life of the cancer patient and their loved ones.4

Cancer is caused by the excessive growth of abnormal body cells. These abnormal cells clump together to form a tumour at a specific site in the body (e.g. the breast or the prostate). The tumour grows larger and becomes more dangerous if it is not treated. Once a cancerous tumour forms, abnormal cancer cells can move from the tumour site (e.g. the breast or prostate) to other places in the body.5

Cancer cell growth occurs when the processes of the cell cycle that usually regulate how many new cells the body produces, and ensure those cells are healthy, dysfunction.5 Understanding the healthy cell cycle is an important foundation for understanding the abnormal cell growth processes of cancer. For more information see The Cell Cycle.

How do cancer cells differ from healthy body cells?

Cancer cells are abnormal cells which avoid programmed death (also referred to as apoptosis). They differ from healthy body cells both in terms of their molecular composition (the proteins and DNA they contain) and their growth pattern (their progress through the cell cycle).5 Genes often play an important role in cancer, but there are many cancers where only a very few mutations are present and the main defect is a breakdown of the normal interactions between the molecules in the cell.

Cancer cell composition

The composition of DNA, RNA and proteins in cancerous cells differs from the composition of healthy body cells. These differences are referred to as molecular changes and include mutations.6 Cancer cells typically have around 60 different mutations, only some of which make them cancerous.5

These mutations typically include: 5

  • Abnormalities that promote more rapid cell growth. Effectively this means that the cancer cell can reproduce itself more often than a normal healthy cell; and
  • Abnormalities which prevent mutations in the genes being recognised. This means that the cancerous cells avoid being programmed to die.

The combination of more rapid cancer cell growth and cancer cells avoiding programmed death leads to an excessive number of cancer cells. They form a tumour at a specific body site, and may over time spread to other body sites.5

Cancer cell life cycle

Cancer-causing changes in molecular interaction and mutations in cells give them an advantage over normal healthy cells, because they can reproduce themselves more rapidly and compete with healthy cells more effectively. The changes in cancer cells influence their growth pattern, enabling them to grow more quickly and avoid being programmed to die. Cancerous cells can escape the checks and balances that normally regulate cell growth and death.6 For example, in normal cells, components of DNA called tumour suppressor genes prevent the uncontrolled growth of cells. These genes send signals that cause cells which are too old or have abnormalities to die. Mutations or functional defects in tumour suppressor genes prevent them from fulfilling cell growth regulating functions, in turn allowing abnormal cells that can form cancer tumours to proliferate.5

The more that cancerous cells divide and replicate over time, the more functional alterations and mutations they typically contain. Effectively this means that cancerous cells grow and spread more rapidly over time and cancer becomes more aggressive and difficult to treat the longer it is left untreated. They may develop the ability to metastasise, or spread to other sites in the body. For example, a cancer that started growing in the breast may spread to the liver.5

What are cancer biomarkers?

Cancer biomarkers are markers (signs) found in the blood, bodily fluids or tissue which indicate something abnormal is happening in the body, such as cancer. There are also biomarkers of other diseases such as heart conditions. Biomarkers may help health professionals to:7

  • Identify individuals who have an increased risk of cancer;
  • Diagnose new cancers or those which return after treatment;
  • Identify the body site in which cancer cells originated;
  • Determine a patient’s prognosis (how the disease is likely to affect the patient);
  • Identify the most appropriate treatment and the likelihood different types of treatments will be effective;
  • Monitor a patient’s response to treatment.

Biomarkers play an increasingly important role in cancer management, and technological advances mean that new biomarkers for cancer are constantly being identified.7



  1. Global, regional, and national cancer incidence, mortality, years of life lost, years lived with disability, and disability-adjusted life-years for 32 cancer groups, 1990 to 2015: A systematic analysis for the Global Burden of Disease Study. JAMA Oncol. 2017;3(4):524-548. [Full text]
  2. Australian Government Cancer Australia. All cancers in Australia. 2017 (cited 26 March 2017). Available from: [URL link]
  3. Ministry of Health New Zealand Government. Cancer. 2017 (cited 26 March 2017). Available from: [URL link]
  4. Garvey G, Thewes B. The effects of cancer on social and emotional wellbeing. Cancer Institute of NSW; 2016 (cited 26 March 2017). Available from: [URL link]
  5. O’Connor C, Adams JU. Unit 5: How do cells know when to divide? Essentials of Cell Biology. Cambridge, MA: NPG Education; 2014. [Book]
  6. Mayo Clinic. Cancer: Causes. 2015 (cited 21 April 2017). Available from: [URL link]
  7. Henry NL, Hayes DF. Cancer biomarkers. Mol Oncol. 2012;6(2):140-6. [Full text]
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