Can Breast Milk Predict Cancer Risk?

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I’m attending the annual meeting of the American Association for Cancer Research in Orlando, Fla., where an interesting study was presented Monday about the potential of breast milk to help, of all things, prevent cancer.

Kathleen Arcaro, a professor veterinary and animal sciences at the University of Massachusetts-Amherst, announced today that when looking for the earliest signs of breast cancer, breast milk might prove as useful as other methods like screens and biopsies, which are more sophisticated — and more invasive.

Arcaro is reporting the preliminary results of her ongoing study of 250 women in 41 states, all of whom are at high risk of breast cancer and have either already had or are planning to have biopsies of their breast tissue. All are also nursing and agreed to provide breast milk for the study.

Arcaro decided to study breast milk because retrieving other sources of breast tissue using needles is not only invasive, but also provides only a snapshot of the cells in one area of the breast. Breast milk, she reasoned, contains millions of cells shed by various parts of the breast and therefore would serve as a better representative of any cancer activity occurring in the tissue.

Arcaro also relied on a growing body of data that shows that the DNA of malignant cells take on a distinct epigenetic profile as a result of a molecular process known as methylation: essentially, methyl groups attach to DNA to turn genes on or off, and in cancer cells, more of these groups bind to the DNA. In fact, dozens of genes are methylated in this way in various cancers. By looking for the presence of methylation in cells in breast milk, Arcaro figured, she could get an idea of how potentially cancerous the breast tissue is. And because this process occurs in the early stages of the disease, informing women of their methylation status may help them to take steps to lower their cancer risk.

“We found that examining methylation in breast tissue is a good way to assess individual risk of developing breast cancer,” she says.

She and her team compared methylation rates of a dozen genes associated with breast cancer in breast-milk samples from both the biopsied and non-biopsied breasts of the women at high risk. (Breasts were tested by biopsy if they harbored a possible tumor.) Arcaro found that methylation rates in cells in breast milk from the biopsied breasts were higher than rates in the breasts that weren’t sampled.

For comparison, the scientific team also looked at methylation rates in 102 healthy women from a previous study, who showed low levels of methylation in the same 12 genes. Even after controlling for other factors such as environmental exposure that could affect methylation rates, the relationship remained strong.

Does that mean that mothers might be passing tumor cells on to their babies while they feed? “One hundred percent no,” says Arcaro, who notes that any proteins infants ingest are digested and broken down in the stomach and digestive tract. “The baby would just treat any methylated cells like any protein and digest it,” she says.

How do these results help women? Clearly, they will have the biggest impact on those who are pregnant or nursing. And that’s an important group, says Arcaro, since more women are delaying childbirth and the risk of cancer goes up with age. If the results hold with repeated studies, she anticipates that breast milk screening might become a noninvasive way that all mothers giving birth could be screened for breast cancer before they leave the hospital. “It’s totally noninvasive, potentially inexpensive and really accurate,” she says. So what’s healthy for Baby might be good for Mom as well.

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