What is cancer?

Sunday 1 February, 2015

Cancer is a disease of the cells, which are the body’s basic building blocks. The body constantly makes new cells to help us grow, replace worn-out tissue and heal injuries. Normally, cells multiply and die in an orderly way.

Sometimes cells don’t grow, divide and die in the usual way. This may cause blood or lymph fluid in the body to become abnormal, or form a lump called a tumour. A tumour can be benign or malignant.

  • Benign tumour:Cells are confined to one area and are not able to spread to other parts of the body. This is not cancer.
  • Malignant tumour: This is made up of cancerous cells, which have the ability to spread by travelling through the bloodstream or lymphatic system (lymph fluid).

How cancer starts

A diagram of cancer cells

The cancer that first develops in a tissue or organ is called the primary cancer. A malignant tumour is usually named after the organ or type of cell affected.

A malignant tumour that has not spread to other parts of the body is called localised cancer. A tumour may invade deeper into surrounding tissue and can grow its own blood vessels (a process known as angiogenesis).

If cancerous cells grow and form another tumour at a new site, it is called a secondary cancer or metastasis. A metastasis keeps the name of the original cancer. For example, bowel cancer that has spread to the liver is called metastatic bowel cancer, even though the person may be experiencing symptoms caused by problems in the liver.

How cancer spreads

A diagram of cancer cells spreading 

Find out more about symptoms of specific types of cancer look in our cancer types section.


Adapted from Understanding Bowel Cancer

Reviewed by: Mr Chip Farmer, Colorectal Surgeon, The Alfred Hospital, Cabrini Hospital and The Avenue Hospital, VIC; Mervyn Bartlett, Consumer; Dr Andrew Haydon, Medical Oncologist, The Alfred Hospital and Cabrini Hospital, VIC; Jackie Johnston, Palliative Care and Stomal Therapy Clinical Nurse Consultant, St Vincent’s Private Hospital (Darlinghurst), NSW; Dr Shahrir Kabir, Fellow in Colorectal Surgery, Royal Brisbane and Women’s Hospital, QLD; Steve Pratt, Nutrition and Physical Activity Manager, Cancer Council WA; Cassie Riley, Cancer Nurse Coordinator – Colorectal, WA Cancer and Palliative Care Network, WA; Mary Shanahan, Cancer Genetics Nurse Coordinator, Peter MacCallum Cancer Centre, VIC; A/Prof Andrew Stevenson, Head of Colorectal Surgery, Royal Brisbane and Women’s Hospital, University of Queensland; Pat Walls, Clinical Nurse Consultant Stomal Therapy/Wound Management, Holy Spirit Northside Private Hospital, QLD.

Updated: 01 Feb, 2015