Large Study Identifies 65 New Indicators of Breast Cancer Risk

Your risk of developing breast cancer and many other conditions is determined in part by your unique genetic code. Maybe you have heard of the infamous “BRCA1” (BReast CAncer 1) gene, discovered in the early 90s which has strong associations with a woman’s risk to develop cancer. Among other risk factors, the BRCA1 gene can account for why breast cancer can “run in the family”.

In a new study published by Nature, Michailidou et al. have identified 65 new genetic signatures which influence your risk for breast cancer. The study, which involved almost 300,000 patients and healthy people (studies have to look at women with breast cancer and women without breast cancer to be able to compare the two groups), authors have found 65 new loci in the genome which are associated with breast cancer.

In genetics, a locus (plural: loci), is a location in our DNA. All humans, to a remarkably high extent, have very similar DNA sequences. Therefore, our genomes, an overall map to our DNA, by-and-large look the same. The differences between people’s DNA can account for many of the differences in humans, like the color of our eyes, how much alcohol we can handle, and in this case, how likely we are to develop certain diseases.

In this paper, what the authors have done is compare the genomes (the sum total of their DNA) of patients with breast cancer to women who don’t have breast cancer in order to identify where those people’s DNA differs. By comparing these two groups, the scientists were able to find 65 different loci, or locations in the human genome, which were associated with risk for breast cancer. At these loci, most people have one specific nucleotide (the building blocks of our DNA), but if you have a different one, you may be at an increased (or even a decreased) risk for developing breast cancer. In most of these locations, the risk factor is what’s called a “Single-Nucleotide Polymorphism” or SNP (Single=1, Nucleotide=building block of DNA, Polymorphism= occurs in different forms). So for that particular location, some people have a different nucleotide than others.

But what does that mean for people who have these specific mutations? Are you doomed to get breast cancer later in life? How much has your risk increased?

A few years ago BRCA1 found itself in the news again when prominent actress Angelina Jolie found out she had a risky mutation (a change in her DNA code) in BRCA1. Jolie took preemptive measures and opted for a double mastectomy, to largely eliminate the risk. To many people (including scientists!) this may seem like a drastic move considering the fact that she didn’t actually have breast cancer.

In preparing to write this short summary, I spoke to a colleague and genetic counselor about how to discuss genetic “risk” for diseases. In a new era of medicine, where a person’s genetic code might be used (or abused) to tailor their treatment, there is a lot of discussion about what information people should have access too. On one hand, it is argued that your genetic code is your personal data which you should have access to. On the other, most genetic counselors would argue that people need to be educated about what their genetic code could mean. Imagine, for example, if you found out you have an increased risk for breast cancer, a disease which claims tens of thousands of lives a year, you might decide that a double mastectomy is worth not having to worry. But what if you found out, after the mastectomy, that you actually only had a 0.02% increased risk for breast cancer? Suddenly the mastectomy seems like a bit of a rash decision.

The point that is important to drive home is that, while these 65 new loci are associated with increased breast cancer risk, they wouldn’t necessarily indicate that someone with mutations at those locations will get breast cancer.

The key points of this paper include the size of the study, which strengthens the claims they make, and the novelty of these loci. With the identification of more risk loci and a deeper understanding of the genetics of cancer, it will become easier to catch cancers early, and to personalize their treatment, both of which contribute to less deaths from the disease.

Some weaker points of the paper might be that they used almost exclusively european and asian women’s genetic material. Although most of these risk loci are probably universal to women of all races and genetic backgrounds, there is a great deal of nuance which can be attributed to other factors including race, environment, and socioeconomic status. Further, the authors have provided a huge amount of data in this study, but it will take much more research before all of that data can be made useful to clinicians trying to treat cancer patients. That’s why it is important that we continue to fund science research!

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