Breast cancer is the most common type of cancer among women—a woman born in the U.S. today is estimated to have a one in eight chance of developing breast cancer. One way to predict who will develop breast cancer is to test for mutations in the BRCA-1 and BRCA-2 genes, which can increase a woman's chances of developing cancer to as high as 85 percent.
However, BRCA mutations only account for about 10 percent of all cases of breast cancer. So how can doctors predict breast cancer the other 90 percent of the time?
Scientists are going beyond mammograms and genetic tests to develop a blood test that can predict which women will develop breast cancer years in advance.
In a paper published in Genome Medicine, a team of researchers from University College London (UCL) found an epigenetic signature that is associated with all breast cancer cases, not just those that are linked to a BRCA mutation.
"We identified an epigenetic signature in women with a mutated BRCA-1 gene that was linked to increased cancer risk and lower survival rates,” said Professor Martin Widschwendter, the study's lead author and head of UCL's Department of Women's Cancer, in a press release. “Surprisingly, we found the same signature in large cohorts of women without the BRCA-1 mutation and it was able to predict breast cancer risk several years before diagnosis."
Although your DNA, called the genome, determines what proteins your body’s cells can produce, you also have an epigenome, a series of molecules that attach themselves to your DNA to increase or decrease the activity of specific genes. The most well-studied form of epigenetics is methylation, in which environmental factors cause methyl groups to bond to DNA.
Usually, the methyl groups bond with the promoter region of a gene, a set of DNA at the beginning of the gene that instructs the cell to turn the gene on. Methyl groups tend to downregulate genes, meaning that if a promoter normally instructed a gene to express itself 20 times, a methylated gene might only express itself 10 times instead.
In humans, most epigenetic changes occur during fetal development and early childhood, and they are influenced by any number of environmental factors.
An Epigenetic Difference
To find an epigenetic signature linked to breast cancer, the scientists examined a large group of blood samples from women with a certain cancer-causing BRCA-1 mutation. Among the women who went on to develop breast cancer, they found that a certain gene cluster was methylated.
The genes in question are involved in helping stem cells to differentiate. Stem cells can divide endlessly and become any type of cell the body might need. If this process goes awry and these super-cells start working against the body instead of for it, the result is cancer. Although the exact process is unknown, methylation of these genes is linked to higher rates of cancer.
But the real question was, do women without a BRCA-1 mutation who go on to develop cancer also have these same methylated genes? The researchers were surprised and pleased to discover that they do.
Widschwendter’s team isn’t yet sure whether the methylated DNA is one of the factors that directly causes breast cancer, or if the methyl signature is just a handy biomarker. Still, his team's research could be part of a new wave of early breast cancer detection.
“The data is encouraging since it shows the potential of a blood based epigenetic test to identify breast cancer risk in women without known predisposing genetic mutations,” he said.