UT Southwestern Medical Center researchers have found that a chemical reaction in the genes may actually provide a molecular clock that could determine a woman's risk of developing breast cancer.
In a study published in today's issue of Cancer Epidemiology Biomarkers and Prevention, scientists from UT Southwestern show that the chemical process, called methylation, is strongly correlated with breast-cancer risk and with precancerous changes in the breast cells.
The researchers determined that methylation acts as a type of biological clock, indicating how many times a cell has divided. This information could aid researchers in determining an individual's cancer risk.
"The more a cell has divided, the greater the risk for cancer," said Dr. David Euhus, professor of surgical oncology.
"Monitoring methylation levels could give researchers a way of seeing how often cells have divided and where a woman stands on that clock. Once the clock reaches a certain hour, breast cancer is more likely to ensue," he added.
During methylation, small molecules called methyl groups attach themselves to a gene and turn off, or "silence," the gene.
In the study, Dr. Euhus wanted to see if methylation of RASSF1A and other genes increased over time during the years when the ovaries are actively secreting estrogen and progesterone each month.
Dr. Euhus and his team sampled cells from 164 women - women with breast cancer, women at high risk of developing breast cancer, and women with a low risk for the disease.
The researchers examined methylation levels of five tumor-suppressor genes whose job is to stop tumors from developing in the breast.
A computer program developed by Dr. Euhus was used to determine the breast-cancer risk for patients in the study. His findings indicate that methylation of RASSF1A and other genes increases steadily during the years of ovarian cycling - up to about age 55 - suggesting that methylation is, indeed, a molecular clock recording the history of cell divisions.
"Interestingly, having children, which is known to reduce breast-cancer risk if it occurs early in life, was associated with a reduction in methylation for some genes," Dr. Euhus said.
Dr. Euhus says the clock is not always marching forward, and there are ways to turn it back.