DNA and Age-Related Cancers

By Jane Farrell

Changes in a process that controls genes appear to be linked to some of the increased risk of cancer seen in older people, according to a new National Institutes of Health study.

It’s long been known that age is a leading risk factor for the development of many cancers. But scientists haven’t known exactly why that’s so. They’ve suspected a process called DNA methylation– the binding of chemical tags, known as methyl groups, onto DNA.

Now, Zongli Xu, Ph.D., and Jack Taylor, M.D., Ph.D., researchers from the National Institute of Environmental Health Sciences (NIEHS), part of NIH, have demonstrated that cells that become increasingly methylated with advancing age are also disproportionately represented in a variety of human cancers.

The findings were published in the journal Carcinogenesis.

"You can think of methylation as dust settling on an unused switch, which then prevents the cell from turning on certain genes," Taylor said. "If a cell can no longer turn on critical developmental programs, it might be easier for it to become a cancer cell.”

For the study, researchers looked at blood samples from 1,000 participants in the Sister Study, a nationwide research effort to find the environmental and genetic causes of breast cancer and other diseases. More than 50,000 sisters of women who have had breast cancer are taking in the study.

The analysis showed that nearly one third of the samples showed age-linked DNA methylation.

The researchers found that 70-90 percent of the sites associated with age showed significantly increased methylation in seven cancer types. Taylor suggested that age-related methylation may disable the expression of certain genes, making it easier for cells to transition to cancer.

"The longer you live,” Xu said, “the more methylation you will have."

In future research, Xu and Taylor want to examine more samples, breaking down data from the cells still further.