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New genetic variants associated with breast cancer identified

4:00pm Wednesday 25th October 2017 content supplied byNHS Choices

"Do you have one of the 180 breast cancer genes? One in five women has a variant that raises her risk of the condition by a third" is the rather inaccurate headline in the Mail Online.

The story covers 2 new studies looking for genetic variations known as single nucleotide polymorphisms (SNPs).

These are small variations in our DNA, some of which are associated with an increased risk of developing a disease - in this case, breast cancer.

While the Mail Online's headline suggests the "breast cancer genes" have been pinpointed, this is not the case.

In most cases, the genetic variations identified by the researchers simply signpost regions in the DNA (loci) where the genes that affect breast cancer risk are likely to be located.

This is not the same as identifying specific genes or discovering why they increase the risk of breast cancer.

The individual variations identified are only associated with small increases in risk, and many women will carry them.

This is very different from the mutations in the BRCA1 or BRCA2 genes, which cause breast cancer - these are rare and have a bigger impact on risk.

These findings are useful steps towards understanding more about which genes influence breast cancer risk.

But while they may eventually pave the way towards more targeted screening strategies, the research is still at a relatively early stage.

You can't change the genes you're born with, but there are things you can do to reduce your risk of getting many types of cancer, such as quitting smoking if you smoke, taking regular exercise, maintaining a healthy weight, and drinking alcohol in moderation.

Where did the story come from?

The headlines are actually based on 2 related research papers.

One study looked at breast cancer as a whole, and the second, smaller, study looked at a specific type of breast cancer known as oestrogen receptor negative breast cancer.

Together, the 2 studies looked at data on 275,000 women.

This analysis focuses on the first, larger study.

The study was carried out by researchers from several international institutions, including the University of Cambridge in the UK and the University of Washington School of Public Health in the US.

It was published in the peer-reviewed journal Nature.

The study was funded by a large number of organisations, including charities, educational institutions and government agencies.

Some of the media headlines covering this study are misleading. For example, the Sun suggests that, "More women [are] at risk due to discovery of further cancer causing gene mutations".

This poorly worded headline suggests women's level of risk has somehow risen.

The study has helped us understand more about women's risk, but their risk hasn't changed: it's the same.

And hopefully as we learn more about the genetics of breast cancer we may be able to find ways to reduce this risk.

The study also didn't identify "180 breast cancer genes". The results just signpost where in the DNA these genes are likely to be.

What kind of research was this?

This study is what's known as a genome-wide association study. This involved studying the human genome - the complete set of DNA present in a human.

The researchers looked at small variations in DNA. These variations are known as single nucleotide polymorphisms (SNPs, pronounced "snips").

Most SNPs don't affect a person's health or characteristics. But they can help researchers find genes that affect people's risk of disease.

Some SNPs are more common in people who have a specific condition (such as breast cancer) than those without the condition.

This indicates that the regions of DNA surrounding these SNPs are likely to contain genes that are contributing to these diseases.

What did the research involve?

The researchers analysed data from 78 genome-wide studies: 67 European and 12 Asian ones.

The studies included data on the DNA of about 256,000 women, about 137,000 of whom had breast cancer.

The researchers analysed information on around 21 million genetic variations.

What were the basic results?

The main finding was the identification of SNPs in 65 new regions of DNA (loci) associated with an increased risk of breast cancer.

The researchers then carried out various analyses to look at which genes lay nearby and could be responsible for the links found.

They found almost 700 genes of interest, including some already known to be involved in breast cancer.

How did the researchers interpret the results?

The researchers concluded: "These results provide further insight into genetic susceptibility to breast cancer, and will improve the use of genetic risk scores for individualised screening and prevention."

Conclusion

This large analysis of data has identified 65 more SNPs associated with an increased risk of developing breast cancer.

These variations hadn't previously been associated with overall breast cancer risk.

A second, smaller study published at the same time identified another 7 variations specifically associated with an increased risk of oestrogen receptor negative breast cancer, a type of breast cancer that's notoriously hard to treat.

In total, these studies bring the number of SNPs associated with breast cancer to about 180.

Although these are interesting findings, there are a few points to bear in mind:

  • The variations investigated in this type of study don't usually cause the increase in risk. Instead, they usually lie near a gene that's actually affecting the risk. Researchers have started to look for these genes, but as yet we can't say this specific piece of research "found 180 breast cancer genes".
  • The individual variations identified are only associated with small increases in risk, and many women will carry them. This is very different from the mutations in the BRCA1 or BRCA2 genes that cause breast cancer - these are rare and have a bigger impact on risk.
  • The researchers and some of the news sources suggest that this study's findings could help with the early detection and prevention of breast cancer. While this may be the case in the longer term, it's still early days when it comes to using this data for recommending preventative treatment like mastectomy.

Professor Karen Vousden, chief scientist at Cancer Research UK commented: "The results, gathered from around the world, help pinpoint the genetic changes linked to a women's risk of breast cancer.

"Learning which women are at higher risk of breast cancer could help identify who may benefit from earlier screening, and spare women at a lower risk from having to attend screening if it's unlikely to benefit them."

Summary

"Do you have one of the 180 breast cancer genes? One in five women has a variant that raises her risk of the condition by a third" is the rather inaccurate headline in the Mail Online.

Links to Headlines

Breast cancer study uncovers new genetic variants for increased risk. The Guardian, October 23 2017

Scientists find some of the genetic variants responsible for increasing womens' chance of breast cancer. The Independent, October 23 2017

Do you have one of the 180 breast cancer genes? One in five women has a variant that raises her risk of the condition by a third. Mail Online, October 23 2017

Links to Science

Michailidou K, Lindström S, Dennis J, et al. Association analysis identifies 65 new breast cancer risk loci. Nature. Published online October 23 2017

Milne RL, Kuchenbaecker KB, Michailidou K, et al. Identification of ten variants associated with risk of estrogen-receptor-negative breast cancer. Nature Genetics. Published online October 23 2017

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