Breast cancer gene study is a step forward, but tests are still some way off

The new breast cancer gene variants are pieces of a bigger jigsaw puzzle

Last week, researchers announced that they’d homed in on five more variations in our genetic code that are linked to a slightly increased risk of breast cancer. Cancer Research UK, together with the Wellcome Trust, funded the study, which was published in Nature Genetics.

And, despite the post-election negotiations dominating the news, the study was reported in the national media, for example in the Guardian and on BBC News.

We were going to write about this research on this blog, but the ever-excellent Behind the Headlines crew over at NHS Choices got there first. Here’s their (edited) take on it – please do read their whole post if you have time:

The study …investigated the association between genetic variants and breast cancer. It included only women who had both breast cancer and a family history of the disease. Genome-wide association studies, a form of case-control study, provide a way to examine the association between genetic factors and disease.

The researchers explain that recent studies have identified 13 variants that are associated with an increased risk of breast cancer. However, they say that these appear to play only a small role in the approximately doubled risk of breast cancer seen in first-degree relatives of affected women. Their study was an attempt to identify additional variants.

The researchers recruited 3,659 [women with breast cancer], all with a family history of the disease. The women’s genetic codes were analysed and compared with those from 4,897 control women who did not have breast cancer.

A second group of cases and controls was recruited to validate the associations seen in the first phase. This included 12,576 cases and 12,223 controls. In this second phase, the researchers specifically assessed the contribution of the 15 variants that they found to be linked with breast cancer in their first analysis. The variants studied did not include those that were already known through prior research. In this second part of the study, the cases were women with breast cancer but not necessarily a family history of the disease.

In the first phases, the study found a significant association between breast cancer and seven different genetic variants, all of which had been linked with the disease in previous research. Therefore this finding confirmed known associations.

In the second phase of their study, the researchers identified five new variants (on chromosomes 9, 10 and 11) that were associated with disease.

In recent years, researchers around the world have been making huge strides in finding small genetic variations that are linked to diseases like cancer – so much so that studies like these are now commonplace. Indeed, Doug Easton, one of the researchers involved in this work, has previously pinned down gene variants linked to several forms of cancer, including breast, prostate and testicular cancers.

The real challenge now is to turn this knowledge into clinically useful tests that can help doctors deal with cancer and help patients beat the disease – and that still seems to be a few years away.

One big hurdle to overcome is that researchers don’t yet know all the genetic variants that affect risk – so at best the overall picture is incomplete. It’s a bit tricky to work out the picture on a jigsaw if you only have half the pieces – and as this research shows, new bits of the puzzle are still being discovered.

Direct-to-consumer testing

Nevertheless some companies are already selling tests, based on this type of research, directly to the public, as we’ve written about before.

Our concern is that it’s hard for people to tell the difference between high-quality tests and ones based on lower-quality data. The US Government recently announced plans to set up a genetic testing registry (discussed in this excellent post on the Genomics Law Report blog) to help solve this problem – and we at Cancer Research UK would support moves to do similar in the UK. People need to know that what they’re buying is scientifically accurate and well-run.

On top of this, there’s still the question of what to do with the results of these tests. In the here-and-now, knowing exactly which genetic variants you carry isn’t a huge amount of practical use – the things you can do to reduce your cancer risk are essentially the same.

One future possibility is to offer targeted screening to people with certain genetic variations. Another is that gene variants could help doctors choose which treatment regime is most suitable for a given patient.

But to get to this point, we need many more, well-funded, well-conducted studies to turn the ever-growing mountain of data about our genes into practical, helpful, life-saving healthcare.

Henry

Reference:

Turnbull, C. et al (2010). Genome-wide association study identifies five new breast cancer susceptibility loci Nature Genetics DOI: 10.1038/ng.586