WASHINGTON, DC —Researchers from Georgetown Lombardi Comprehensive Cancer Center demonstrate, in animals, that maternal exposure to a high-fat diet or excess estrogen during pregnancy can increase breast cancer risk in multiple generations of female offspring — daughters, granddaughters and even great-granddaughters.
This study, published online today in Nature Communications, shows for the first time that the risk of some "familial" breast cancers originate from biological alterations caused by maternal diet during pregnancy that not only affect the directly exposed fetus but also the fetal germ cells, transmitting the increased mammary cancer risk to subsequent generations.
This study also provides some hints about the biological mechanisms behind this multi-generational transmission of risk. The researchers found that maternal intake of high-fat diets and excess estrogens changes DNA methylation patterns in the offspring's breast and make it more sensitive to carcinogens later in life. Importantly, these traits are inheritable.
"We know that maternal diet can have long lasting effects on an offspring's health, but this study demonstrates, for the first time, that a high fat diet or excess estrogen can affect multiple generations of a rat's offspring, resulting in an increase in breast cancer not only in their daughters, but granddaughters and great granddaughters," says the study's senior investigator, Leena Hilakivi-Clarke, Ph.D., a professor of oncology at Georgetown Lombardi.
The research team, which includes investigators from institutions in Finland and the United States, tested three groups of pregnant rats and their progeny. The two exposed groups of rats were at heightened risk for developing breast cancer, compared to the control group.
In the first group, rats were fed a high fat diet before conception and throughout pregnancy. Breast cancer risk was increased by 55 to 60 percent in the daughters and granddaughters of rats given a high fat diet during pregnancy compared to the offspring of control rats which ate a normal diet during pregnancy. The increased risk did not extend to the great-granddaughters of high-fat fed rats.
"We also found that if the mother was fed a high fat diet before conception and throughout pregnancy, the risk of increased breast cancer was transmitted to granddaughters through either males or females exposed to the high fat diet in utero," says the study's lead investigator, Sonia de Assis, Ph.D., a postdoctoral researcher in Hilakivi-Clarke's laboratory.
In the other group, rats were fed a diet supplemented with estrogen during the last week of pregnancy, and the control rats were fed a normal diet. The researchers found a 50 percent higher incidence of breast tumors in the exposed rats' daughters, granddaughters, and great-granddaughters, compared to the control group. In this case, increased breast cancer risk was transmitted to granddaughters through the in utero estrogen exposed females only.
Both the high-fat and excess estrogen diets produced breast tissue in the affected generations of female offspring that had more than the normal number of terminal end buds, structures that are the building blocks of mammary epithelial tree and primary targets for carcinogens.
The researchers also documented epigenetic changes in the mammary glands of all three generations of pregnant rats exposed to estrogen.
"Germ cells — cells involved in reproduction — first develop during the fetal period and in utero exposures, such as the ones in our study, could disrupt their normal epigenetic marks and affect how genes are turned on or turned off," de Assis says. "Those alterations then can be passed on and affect the risk of disease, in this case breast cancer, in subsequent generations."
Hilakivi-Clarke points out that two-thirds of human familial breast cancers have no known genetic mutations. She says the effect seen from a high-fat diet and excess estrogens may help explain some of those cases and link them to inherited epigenetic changes.
"We know from human studies that daughters whose mothers took the synthetic estrogen diethylstilbestrol (DES) to reduce pregnancy complications, or who had a birth weight of more than 8.8 pounds are at an increased risk of developing breast cancer. Our study suggests their offspring may also be at risk," Hilakivi-Clarke says.
"This study suggests directions for future research in women. Could a woman's susceptibility to breast cancer development be determined by what her grandmother ate when she was pregnant, or if she was exposed to high levels of estrogen — perhaps unwittingly, through the environment?" asks de Assis.
The researchers add that there is potential good news — epigenetic inheritance of breast cancer risk might be detectable through blood testing, and that, in particular, the adverse effects of an exposure to excess estrogen in utero is, possibly, reversible.
"Our on-going preclinical studies have found that the increase in breast cancer risk caused by in utero exposure to excess estrogens can be reversed by drugs that reverse epigenetic marks — chemical modifications that turns genes on and off — caused by the exposure . These drugs, called HDAC and DNMT inhibitors, are being used, with success, in humans to treat some cancers," Hilakivi-Clarke says. Hilakivi-Clarke is one of the inventors on Georgetown University-owned HDAC inhibitor and DNMT inhibitor patents.
"It's easy to see how this study possibly has human health implications to be considered since fatty foods are endemic in our society, and low levels of chronic exposure to endocrine disruptors — substances that have hormonal activity such as estrogen — have been found in food and drinking water," says de Assis.