What is cancer?

What is cancer?

If your child has recently been diagnosed with cancer, you'll probably want answers to some general questions about cancer - about how it develops, how it is treated and what terms like 'remission' actually mean.

Key points to remember

This page is part of a whole section 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 is normal cell growth?

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 (for example, kidney, muscle) 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 or DNA for short. DNA is divided up into structures called chromosomes. Humans have 46 chromosomes, 23 from each parent. Each chromosome is made up of sections or 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.

What is cancer growth?

Cancer develops when a cell in the body, for some as yet unknown reason, 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. It is not known when a cancer really begins, but there is always a period of time before it becomes noticed.

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 soft tissue-like muscle)
  • osteosarcoma and Ewing's sarcoma (bone cancers)
  • Wilms tumour (a type of kidney cancer)

Childhood cancers are rare, affecting approximately 1 in 10,000 children per 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 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. 

Cancer is not catching (contagious). There is therefore, 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.

Treatment and cure

The aim of treatment for most childhood cancers is cure. There are still many unanswered questions about cancer, which makes 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 or several months.

What is a 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 be seen by 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. Further treatment is required over many weeks or months to destroy the remaining cancer cells.

Different lengths of time are needed to treat different types of childhood cancer. Your doctor will explain the length of time required for your child's treatment and follow-up. It can take a number of years before it can safely be said that there has been a cure.

What is 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 that a new treatment approach must be taken. Throughout the course of treatment and for a long time after treatment is finished, the oncology team will monitor your child for any signs of a relapse.

What are some questions you can ask?

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?

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 20 June 2017.
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