Relatives with cancer? It usually means less than one thinks

Relatives with cancer? It usually means less than one thinks

I was asked to speak on Radio 4's Inside Health this week about how one's cancer risk is affected by having relatives with cancer.

You can hear it here (from 20 mins): BBC Radio 4 – Inside Health, Yellow cards, virtual autopsies, genetics and cancer

Most people overestimate the impact that having relatives with cancer has on their own cancer risk.

There are a number of reasons for this:

  • Cancer is very common, about 1 in 3 people will get cancer. It is therefore entirely expected for the majority of people to have one or more relatives with cancer. Usually this is not because of hereditary factors, it is because cancer is common.
  • The term 'cancer' is used to cover 100s of different conditions, most of which are not linked to each other at all. So usually if there are people with different cancers in a family the cancers will have occurred independently.
  • Cancer is a complex condition, many different factors are involved. Hereditary factors are the major factor in only a small proportion of cancers overall, though they do make a sizeable contribution to some cancers.
  • Many people think 'genetic' means the same as 'hereditary'. This is not the case. Most of the genetic mutations relevant to cancer occur only in the cancer cells, they are not in the rest of the body. They are not in the blood line, have not been inherited and cannot be passed on to children.

If there are lots of cases of the same cancer in a family, or if the cancers occurred much younger than typical for that cancer, or if there are particular combinations of cancers, hereditary factors are more likely to be involved.