Yesterday Angelina Jolie shared her experience as a carrier of a BRCA1 genetic mutation that confers a very high lifetime risk of developing invasive breast cancer. New Scientist spoke to breast cancer specialist Allison Kurian, of Stanford University in California who has developed a tool that enables women to determine how different treatment options can reduce their overall risk.
For carriers of a BRCA1 mutation, the lifetime risk for invasive breast cancer is 65 per cent. What is that based on?
It's based on very large studies of thousands of women. When we're counselling people, we give them average numbers because they're the most robust.
Angelina Jolie said her lifetime risk was 87 per cent, where did that figure come from?
That 87 per cent number is from some of the earlier studies. The BRCA1 and BRCA2 genes were discovered in the mid-90s and the earliest research mostly studied very striking families who came to doctors because everybody had cancer. When you look at those families, you're going to make a very high estimate of risk. But then when you do bigger studies, the average risk is lower.
So that 87 per cent figure is probably not a calculation of her personal risk?
I am not involved with her care, but I doubt it's a personal assessment. I see that number often and in general think of it as coming from slightly older, smaller studies. Most of us in this field tend to use the newer numbers from the larger studies.
From that 65 per cent average, what makes an individual carrier of a BRCA1 mutation more or less likely to get breast cancer?
That's the million-dollar question. There's great interest in understanding why one person with aBRCA1 mutation might develop cancer in their 30s whereas another might never get cancer at all.
But if a woman has a BRCA1 mutation and most of her relatives have developed very early breast cancer, I worry about her a little bit more than a woman in a family with a BRCA1 mutation where, for whatever reason, they don't seem to have as many cancers.
Is there a way to accurately calculate someone's individual lifetime risk of developing invasive breast cancer?
I don't think we're quite there yet. The BRCA decision tool we developed makes the average estimate based on large numbers, because that is the safest thing to do.
The tool then compares different options a person might choose. For example, one might choose preventive mastectomy, like Angelina Jolie did; other women might choose a very intensive screening strategy. Our tool helps to compare those different options and what they would provide in terms of survival and quality of life.
Angelina Jolie wrote in The New York Times that her double mastectomy cut her risk of getting breast cancer to 5 per cent. Is that typical of women who undergo this procedure?
That would be about right. Most of the studies estimate that whatever a person's risk might be, the surgery will reduce that risk by 90-95 per cent. If her risk was about 65 per cent you're going to get down to a single digit number.
Not everyone currently has access to – or can afford – BRCA screening tests. Do you think they should be offered to all women?
I'd certainly like to see expanded access to healthcare of all kinds. But I don't think that every woman needs to be tested for BRCA mutations because they're rare. On average, if you pull people in off the street, about one in 400 would carry a BRCA mutation.
But I think when there are red flags – like early breast cancer, multiple breast cancers, ovarian cancer or male breast cancer – all of those families should be offered genetic testing.
As a geneticist specialising in breast cancer, were you glad to see Angelina Jolie share her experience of being someone with a BRCA1 mutation?
Absolutely, I think she was extremely courageous. I think it greatly increases the opportunity that we would diagnose people who are at high risk and offer them life-saving interventions. I'm very impressed; it's a very generous thing to do.