Possible breast cancer link to DES exposure spurs Boston lawsuit

By Deborah Kotz, Globe Staff

Over the past few weeks, a Boston judge has been listening to arguments on behalf of breast cancer patients who believe their cancers were caused by prenatal exposure to the drug diethylstilbestrol (DES). Their mothers had been prescribed the estrogen medication four or five decades ago when doctors thought it would prevent miscarriages -- before studies found that not only was DES useless but that it caused reproductive tract defects and cancers in girls born to mothers who took the drug while pregnant. (The drug was taken off the market years ago.)

Barbara Bradlee, a 52-year-old interior designer from Reading, joined the lawsuit after her breast cancer was diagnosed five years ago; she believes that her prenatal exposure to DES is to blame since no one else in her family has had breast cancer. “It’s an obvious connection to me,” she said in an interview.

The legal team representing Bradlee and 52 other breast cancer patients from Massachusetts and elsewhere claims there’s enough scientific evidence from animal studies and epidemiological research to prove that the plaintiffs’ breast cancers were likely caused by their hormone exposure.

“The law says that if you put a drug out on the market and it doesn’t work and it increases the risk of breast cancer, then a person exposed to the drug who gets the breast cancer is entitled to compensation,” said attorney Aaron Levine, who is representing the 53 women.

Lawyers for the defendants, which include former DES manufacturers Eli Lilly and Bristol-Myers Squibb, declined to be interviewed, but they argue that the breast cancer link is far from definitive. Representing Eli Lilly, attorney John Brenner stated during his opening comments on September 7 that “it’s something yet to be proven that DES exposure may ... increase the risk of developing breast cancer. That’s a hypothesis; it certainly warrants scientific investigation.”

While the hearing is currently in recess, both sides will present dueling epidemiologists from Harvard over the next two months to debate the merits of the research linking DES to breast tumors. The best study to date, led by Boston University epidemiologist Julie Palmer, found that prenatal DES exposure nearly doubled the risk of breast cancer in women over 40.

Palmer, who declined to discuss the lawsuit, told me in a previous interview for this article that the increased risk is modest -- on par with having a mother or sister with breast cancer. She also said it was far from proven and needed to be confirmed by other researchers.

That’s in contrast to a rare vaginal cancer that’s been strongly associated with DES exposure. A bulk of studies through the years have found that DES daughters have a risk of developing the cancer, called vaginal adenocarcinoma, that’s 40 times greater than the average woman’s risk. About 1 in 1,000 DES daughters developed these tumors, often before they turned 30.

But breast cancer is far more common, so a doubling in risk could increase a woman’s lifetime risk from 1 in 8 to 1 in 4. And it could affect many more thousands of DES daughters -- posing an extreme liability for Eli Lilly and others if the judge rules that the lawsuit can move forward.

That remains to be seen, but DES daughters do have reason to be vigilant when it comes to breast cancer screening, said Dr. Dimitrios Trichopoulos, a professor of cancer prevention and epidemiology at the Harvard School of Public Health who is not involved in the lawsuit or the breast cancer research.

“To me, the study results are quite plausible and what I would have predicted given what we know about DES,” he said. “It’s likely that maybe half of the breast cancers occurring in DES daughters were caused by the drug. Whether there’s proof, no, I can’t say that.”