A new blood test uses DNA methylation to detect and predict the spread of breast cancer

Widschwendter et al. "Methylation Patterns in Serum DNA for Early Identification of Disseminated Breast Cancer." Genome Medicine (2017).
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Early detection of breast cancer can be the deciding factor between successful treatment
and death. But mammography – the most common detection method – doesn't always find
tumors before cancer has spread. Now, using only a sample of blood, an international research
team has found a way to identify fatal breast cancers up to 12 months before they're
usually diagnosed. The blood test can even find cancer before tumors become visible, creating
new possibilities for early treatment.
To develop the test, the researchers first identified DNA signatures specific to breast cancer.
Cancer cells shed small pieces of DNA into the blood. This genetic material carries unique
DNA methylation patterns. DNA methylation is an epigenetic modification, meaning it can
alter gene activity even when the gene's sequence stays the same. Because methylation
patterns change very early in breast cancer development, they offer a promising detection
tool.
The team used computer software along with a special type of DNA sequencing to discover
cancer-specific methylation patterns in 31 tissue samples. These patterns were then tested
in blood samples from women with primary, metastatic, or no breast cancer. This narrowed
down a methylation signature in a single region – deemed EFC#93 – that acted as a marker
for metastatic cancer.
The researchers then looked for EFC#93 methylation in blood samples from 925 healthy
women who developed either fatal or non-fatal breast cancer within 3 years. The marker
was found in 43% of the women with fatal breast cancer 3 to 6 months before they were diagnosed.
In 25% of this group, it was found 6 to 12 months before diagnosis. These results
suggest that even before a tumor is found, if EFC#93 methylation is present in blood samples,
breast cancer has likely already developed and started to spread.
The team also studied blood samples from women with breast cancer before and after
chemotherapy. The results showed that the treatment was far less effective for the women
with EFC#93 methylation, who were more likely to experience relapse and death than those
without the marker.
Although it's not yet clear whether looking at DNA methylation will lead to life-saving treatments,
these findings show that earlier detection of aggressive cancers is possible.

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