What Is Cancer?

What Is Cancer?

If your child has had a recent cancer diagnosis, you'll probably want answers to some general questions - about how cancer develops, how it is treated and what terms like 'remission' actually mean.


Key points to remember about childhood cancer

  • the human body is made up of many millions of tiny building blocks called cells
  • each type of cell has a special function
  • the human embryo before birth is made up of only a handful of cells - these cells divide and multiply and continue to do so throughout life
  • sometimes things can go wrong with the way cells divide and multiply and cancer can develop
  • the aim of treatment for most childhood cancers is cure
  • treatment may include chemotherapy, surgery, radiotherapy and sometimes immunotherapy and bone marrow transplantation

What does normal cell growth involve?

Every human body has millions of cells

The human body is made up of many millions of tiny building blocks called cells. Each organ of the body contains its own special types of cells. Each type of cell has a special function; for example:

  • kidney cells get rid of waste products
  • muscle cells move a joint

Every cell has a central part called the nucleus containing DNA, chromosomes and genes

Every cell has a central part called the nucleus, which contains the genetic material inherited from parents. The nucleus tells each cell how to operate. All the information that is needed to make a human being is contained in the nucleus of every cell, in a molecule called deoxyribonucleic acid (DNA). DNA is contained within chromosomes. Humans have 46 chromosomes. Each chromosome is made up of genes which provide specific orders to the cell.

Cells divide and multiply throughout life

The human embryo before birth is made up of only a handful of cells. These cells divide and multiply in the small embryo and gradually become more specialised until they form structures such as bone and the heart. After this, each cell divides and produces more of its own kind in a controlled way until the baby is born. The process of cells dividing and multiplying continues throughout life in order to replace old cells that have been damaged through wear or injury. Some cells such as skin and bone marrow can do this very quickly; others such as nerve and muscle do it slowly.

Sometimes things can go wrong

You can see that the making of a human being is very complex and it is not surprising that things can go wrong from time to time.

How does cancer develop in children?

Cancer develops when a cell in the body starts to divide and multiply without the normal control. A mistake in the cancer cell's genes tells the cell to grow, divide and multiply. Millions of cancer cells can grow from one cancer cell.

At first nothing may be noticed, but a build up of cancer cells may produce a lump or tumour. Some types of cancer may produce other symptoms such as bruising, tiredness and aching joints. 

What are the most common types of childhood cancer?

Cancer is not one disease, but more than a hundred different diseases, each with its own pattern of behaviour, response to treatment and outcome. The most common types of childhood cancer are:

  • leukaemia (cancer of the white blood cells)
  • lymphoma (cancer of the lymphatic system)
  • glioma and medulloblastoma (brain tumours)
  • neuroblastoma (cancer of the nerve cells)
  • rhabdomyosarcoma (tumour of muscle)
  • osteosarcoma and Ewing's sarcoma (bone cancers)
  • Wilms tumour (a type of kidney cancer)

Childhood cancers are rare, affecting about 1 in 10,000 children each year. With few exceptions, there is no major risk of other children in the same family developing the same cancer. A small percentage of cancers run in families (for example, retinoblastoma).

What causes childhood cancer?

The cause of cancer is largely unknown. Everyone inherits important growth-controlling genes. These genes can either start or stop cell growth and cancer may develop when a mistake occurs. Parents and caregivers usually find it helpful to talk to their doctor about the cause of cancer. 

You can't catch cancer. So, there is no risk of one child passing the cancer on to another. There is no evidence that cancer occurs following a knock or injury. A child's illness is not caused by something done or not done by the child or anyone else.

What is the aim of treatment for childhood cancer?

The aim of treatment for most childhood cancers is cure. There are still many unanswered questions about cancer, which may make it difficult to accurately predict the outcomes for individual children with cancer.

Treatment may include chemotherapy, surgery, radiotherapy and sometimes immunotherapy and bone marrow transplantation.

The goal of treatment is to achieve a complete remission. This may take a few weeks, several months or even years.

What does it mean if my child with cancer is in remission?

Remission means that the cancer is no longer seen on tests.

When this happens it is known that the treatment has destroyed a large number of the cancer cells in the body. It is likely there are some cancerous cells left that are too small to see in any of the tests available at this time. It does not mean that your child has been cured, although it is a step on the road to cure. Your child will need further treatment over many weeks or months to destroy the remaining cancer cells.

There are different treatment times for different types of childhood cancer. Your doctor will explain the length of time your child needs for their treatment and follow-up. It can take a number of years before it's safe to say that there has been a cure.

What does it mean if my child with cancer has a relapse?

Relapse is the term used when despite treatment, the cancer returns.

A relapse is frightening but it is important to know that a relapse does not always mean that your child will not be cured. It means there needs to be a new treatment approach. During treatment and for a long time after the end of treatment, the oncology team will monitor your child for any signs of a relapse.

What are some questions I can ask about my child's cancer?

Questions you may want to ask your child's oncologist at the treatment centre:

  1. What type of cancer does my child have?
  2. How did it start?
  3. How long has my child had it?
  4. Can it be cured?

Read about where to find more information and support

Read more about childhood cancer


All the pages in the childhood cancer section of this website have been written by health professionals who work in the field of paediatric oncology. They have been reviewed by the members of the National Child Cancer Network (NZ). Medical information is authorised by the clinical leader of the National Child Cancer Network.

This page last reviewed 24 June 2021.

Call Healthline on 0800 611 116 any time of the day or night for free health advice when you need it