Dear Annalisa

I am the mother of a healthy four-year-old daughter. My husband’s mother (my daughter’s grandmother) and one of her sisters (my daughter’s great-aunt) have had breast cancer in their early 50s. As far as I know, neither my mother-in-law nor her sisters have been tested for the BRCA genes. 

A few years ago, my mother mentioned genetic testing to my husband’s mother (in the context of whether my husband’s sister, 40, was considering a test). My mother-in-law said in no uncertain terms that she did not understand why my mother thought this would be necessary, and the conversation was abruptly closed. My husband does not have a good relationship with his mother or aunts, and conversations beyond the quarterly catch-up phone calls tend to get heated, or lead to misunderstandings and complaints. 

Should I broach the subject for my daughter’s sake or simply talk to her, when she is old enough to understand the importance of checks and explain that, because of the history of breast cancer on her paternal side, she should be particularly aware of disease and let her decide for herself whether to be tested in adulthood? 

Is this a strong enough family history to justify her (and any other daughters we may have) being tested now, while she is still a child? Or should my husband have a test to see if he has the gene before we decide whether our daughter should be tested?

G, via email

I spoke to Professor Nazneen Rahman, head of the cancer genetics clinical unit at the Royal Marsden Hospital, and it is with her input that I am replying to you.

As you probably know, breast cancer is very common – about one in eight women will get it (men can get it too, of course, but their risk is far lower). There are two major genes linked to familial breast cancer– BRCA1 and BRCA2. Between them, they account for about 20% of familial breast cancers. If a woman has a mutation in one of these genes, then yes, she will be at an increased risk of breast cancer and of ovarian cancer.

Rahman says: “It’s quite common for more than one family member to get breast cancer and usually this is due to chance rather than a mutation in a cancer gene.”

Although to you it must seem alarming that your daughter has two close female blood relatives with breast cancer, overall it is unlikely that this is because they have a cancer gene mutation. With a family history of a grandmother and great-aunt with breast cancer, the likelihood of your daughter having a mutation in the BRCA1 or BRCA2 genes is actually quite small – less than 5%.

Anyway, your daughter is too young to be tested, as her risk of breast cancer before adulthood is negligible. Even if she were an adult, with this family history and her risk being less than 10% she wouldn’t – currently – be offered testing on the NHS. (You need a  risk of 10% or higher to be offered one.) The test itself is a simple blood test that looks for a change (mutation) within the DNA code of the BRCA1 and BRCA2 genes. However, looking for a mutation isn’t simple, as it is like looking for “one spelling mistake in a very large book”, as Rahman explains. Therefore, the results take four to eight weeks to come through, although new methods for reading the DNA code are making it much faster.

Genes are the pieces of our DNA code that carry the instructions that make our bodies function. We have two copies of every gene; one from our father and one from our mother. So, in fact, you don’t need to know if your mother-in-law and her sisters have a gene mutation. Your husband could, in theory, have the test, but he wouldn’t be eligible for it under the NHS test as his chance of having a mutation is too low. If he doesn’t have a gene mutation, then your daughter isn’t at risk, as the mutations cannot skip a generation. If her father does have a BRCA1 or BRCA2 gene mutation, then your daughter has a 50% chance of having inherited it.

It can be alarming to have very close family or friends develop any disease, but you need to keep things in perspective. When your daughter is an adult, the landscape may well have changed: we will probably know much about the causes of cancer and, hopefully, more about how to prevent it. There is likely to be more testing available, and her family medical history may well have changed by then. At that point there is no harm in telling her calmly about her risks (whatever they actually are) and about self-checking etc. She can then make her own decisions about what to do, if anything.

This article was first published in the Guardian Family section on 13th December 2013.