Breast milk may harbor cancer clues

ORLANDO, Fla. — Breast milk may provide a storehouse of genetic data indicating whether a woman is at risk of breast cancer, a new study finds. The findings were reported April 4 at a meeting of the American Association for Cancer Research.

Past studies of breast tissues and fluids have suggested that molecular changes in certain genes can show up in women at heightened risk of breast cancer.

In the new study, Kathleen Arcaro, an environmental toxicologist at the University of Massachusetts Amherst, and her colleagues analyzed milk from 250 women who had had a single breast biopsied to test whether a lump or other swelling was cancerous or benign. The researchers got milk samples from both breasts.

The researchers looked at a specific type of breast cells shed in the milk. They tested three genes in these cells for methylation, a process that often inactivates a gene by chemically disabling its promoter, or start switch.

The scientists have gotten biopsy results so far from 182 of the women. When the researchers measured cells from 13 women who turned out to have breast cancer, these cells had substantially more methylation in a tumor-suppressor gene called RASSF1 than did cells from breast milk from the noncancerous breast.

In the women whose biopsy results did not indicate cancer, methylation of another tumor suppressor gene, called SFRP1, was more common in milk from the biopsied breast than in the other breast. Most of those cases showed nonproliferative lesions or benign proliferative disease. Some women with these diagnoses are at above-average risk for breast cancer in that breast, and the researchers believe that fine-tuning the screen might reveal whether that risk should be monitored.

The breast milk–screening technique is still in the early stages of development. But if enough genes show a substantial effect, such screening could cover a huge portion of women since the researchers estimate 80 percent give birth at some point in their lives.

The researchers haven’t yet settled on the precise makeup of the test. “You wouldn’t expect that every woman would have the same set of methylated genes,” Arcaro says. So, for example, a gene screen might need to include 25 genes, and having a half dozen methylated could indicate increased cancer risk, she says. “I think that’s where we’re going.” The team has identified nine other genes to investigate, but hasn’t analyzed those yet in the breast milk samples.

Certain groups could benefit from a breast milk–based test, she says, such as women with a family history of breast cancer, those carrying a known genetic mutation predisposing them to risk or even women who simply are having their first child after the age of 30.

Breast milk offers an excellent source of genetic information because of its accessibility, says David Sidransky, an oncologist at the Johns Hopkins Medical Institutions in Baltimore who wasn’t involved in this study. “This is not a trivial issue,” he says. If it works, he adds, the technology might also be used in nonlactating women using nipple aspirate, the small amounts of fluid that can be drawn from a breast.