Why can cancer run in families?

THAT'S THE WHY:When you boil it right down, cancer is a disease where genes have gone awry. Not just any genes, but the ones that influence and control how cells grow.

In the vast majority of cancers, the disruptions to those genes arise spontaneously – that’s to say the person wasn’t born with these gene variants, the mutations came about through interactions with the environment.

But in some instances, a gene may be passed down through families that confers a higher risk of developing cancer.

A case in point is BRCA1, the so-called “breast cancer” gene. Normally, the protein encoded by this gene helps to repair breaks that crop up in our DNA. This means it helps to protect against our cells potentially growing amok and forming tumours.

But if the structure of the BRCA1 gene is altered in a way that means it doesn’t work properly, that element of protection is removed.

Another breast cancer susceptibility gene, BRCA2, also makes a protein that acts as a tumour suppressor – and again certain mutations in the gene’s structure can mean it doesn’t offer the usual protection.

That’s why women born with particular BRCA1 or BRCA2 mutations are at increased risk of developing breast or ovarian cancer at a relatively early age.

And because these tumour suppressor gene variants may be passed down in families, their family trees may show a history of such diagnoses.