What causes cancer?

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Learn about possible causes of cancer and the role of genetics in a cancer diagnosis.

Key points

  • The cause of most cancers is unknown.
  • In rare cases, cancer is caused by a mutation in the genes of DNA passed on through family, but this does not guarantee you or anyone else in your family will have cancer.
  • For most teenagers, cancer happens by chance and not as a result of any one thing.

What causes cancer?

Scientists are researching the answer to what causes cancer. For most cancers though, especially cancers in young people, it’s still not known what causes them. We do know that cancer is not contagious. This means that cancer does not spread from one person to the next – you cannot "catch" cancer.


Having cancer yourself does not mean that your siblings, friends or parents will get cancer. Very rarely, cancer can be caused by a mutation in the genes of your DNA that is passed on through your family. A person with this mutated gene does not automatically get cancer, but the risk of developing cancer increases.

Why did I get cancer?

Scientists do not know what causes cancer in young people and your health-care team may not know what caused your cancer.

Many teens with cancer wonder "Why me?" You might wonder whether you did something that caused your cancer or that made you deserve cancer. The answer to both of these questions is NO. Having cancer is not your fault. You did not cause your cancer and you did not do anything to deserve it. Unfortunately, almost all of the time in teenagers, cancer just happens. Getting cancer happens entirely by chance.

You also did not catch cancer from anyone or anywhere else in the way you might catch a cold.

Last updated: September 3rd 2019