Starting in the 1940s, doctors prescribed a synthetic form of estrogen thought to prevent miscarriages and other complications to millions of pregnant women in the United States.

But in 1971, diethylstilbestrol, or DES, was banned by the U.S. Food and Drug Administration after studies linked it to health problems in the children of women who used it, including infertility and a rare form of vaginal and cervical cancer. In the decades since then, children of DES users have sued pharmaceutical companies that produced the drug in courts across the country, accusing them of failing to test DES and misrepresenting it as safe.

A series of new cases proceeding in federal district courts in the District of Columbia and Boston is bringing a relatively untested issue in DES litigation to the forefront — the link between the drug and breast cancer in the adult children of women who used it.

DES cases traditionally have been difficult to pursue because of how long ago the drugs were first prescribed, according to attorneys involved. Medical records are often gone, most of the doctors and original patients have died, and there is little to no documentation linking patient prescriptions to any one pharmaceutical company.

The breast cancer cases present additional challenges, according to Aaron Levine of Washington’s Aaron M. Levine & Associates, lead plaintiffs’ counsel in the breast cancer cases. Unlike some of the other defects associated with DES, such as the rare vaginal and cervical cancer known as clear-cell adenocarcinoma, the type of breast cancer at issue isn’t unique to DES, he said.

Levine, along with other plaintiffs’ lawyers taking on DES cases, is building his case on studies from the 2000s that found higher rates of breast cancer among adult children above age 40 of women who were prescribed DES.

The main defendant, Eli Lilly and Co., has denied any wrongdoing. In its fiscal year 2011 annual report filed with the U.S. Securities and Exchange Com­mis­sion, the company addressed the breast cancer claims, writing, “We believe these claims are without merit and are prepared to defend against them vigorously.” A company spokesman, J. Scott MacGregor, declined to comment further.

More than a dozen other pharmaceutical companies have been sued over DES. Levine said Eli Lilly has historically been the lead defendant because it was a major producer until the drug was taken off the market.

Peter Woodin of JAMS, a longtime court-appointed special master in DES litigation in courts around New York City, said he has seen a drop in new DES cases over the past 15 years. The children of DES users usually developed reproductive tract defects at a young age, he said, so litigation tapered off as they grew older. If plaintiffs prevail in linking the drug to breast cancer in older adult children, he said, “that would change the game.”

Levine has filed 78 breast cancer cases since 2009, and said his firm is evaluating dozens more. The cases were originally brought in the District of Columbia Superior Court or the U.S. District Court for the District of Columbia, but 53 were transferred to the U.S. District Court for the District of Massachusetts in January 2011.

Mediation is scheduled to begin on April 3 in the Boston cases. Sybil Shainwald, who runs a small practice in New York and has represented plaintiffs in DES litigation since the 1970s, said she thinks the pharmaceutical companies “are less willing than ever to settle.”

Given how long ago the drugs were prescribed, she added, “I think the companies thought they would be finished with DES litigation by now.…However, it’s lasted longer, and they’re reluctant to pay.”

CALIFORNIA’S PRECEDENT

The National Cancer Institute at the National Institutes of Health estimates that between 5 million and 10 million people were exposed to DES in the United States, including pregnant women and their children.

Levine said the cases have usually fallen into four categories: the clear-cell adenocarcinoma cases; cases involving infertility; cases involving birth defects in the grandchildren of women who took the drug; and, most recently, the breast cancer cases.

Early DES plaintiffs ran into trouble because they couldn’t produce evidence detailing which pharmaceutical company had produced a given dose of the drug, said Richard Samp, chief counsel of the Washington Legal Foundation.

A 1980 ruling from the California Supreme Court in a DES case known as Sindell v. Abbott Industries changed the landscape for future DES cases. The court laid out a principle known as market-share liability, where companies would bear responsibility for their share of the market for the product in question. In the DES litigation, that meant that, if plaintiffs prevailed, the pharmaceutical companies would each be liable for whatever percentage of the DES supply they sold.

“For the first time in litigation, courts were willing to overlook the general requirement that you’re required to show a direct causal link between actions by the defendant and injury to the plaintiff,” said Samp, who defended pharmaceutical companies in DES cases in the 1980s as an attorney at Shaw Pittman Potts & Trowbridge, which later became part of Pillsbury Winthrop Shaw Pittman.

Levine estimated that he’s handled several hundred DES cases nationwide since the mid-1980s. He said he filed the breast cancer cases in Washington primarily because of the city’s “liberal” statute of limitations rule, which runs three years from the time plaintiffs should have known they were harmed because of allegedly negligent actions. As the children of DES users get older, he said, timing has become a more pressing issue.

He said he joined with the defense to move the first group of 53 breast cancer cases to Boston because they thought it would speed up proceedings. The cases in Washington were assigned to U.S. District Chief Judge Royce Lamberth, and Levine said they were worried that Lamberth’s full docket — especially the notoriously time-consuming cases filed by detainees at Guantánamo Bay — would slow down the litigation.

The judge in Boston who had agreed to take the cases, U.S. Magistrate Judge Marianne Bowler, also has past experience with DES litigation, according to court filings.

Levine said that, even if more cases transfer to Boston, he still would like to keep some cases in D.C. Superior Court, partly out of convenience and also because he thinks local jurors and judges are savvy and can understand complex cases.

“Are [breast cancer cases] tougher? We’ll find out,” he said.

Contact Zoe Tillman at ztillman@alm.com.