Release of Silicone Study Delayed for Years : Health: Independent expert says 1975 mice test indicates substance in breast implants is very toxic. Dow Corning denies product hurt anyone.

Dow Corning Corp. waited almost two decades to disclose an internal study on mice that raised questions about the safety of its silicone breast implants in the mid-1970s.

But implant opponents and the company disagreed Thursday on whether the delay, or the research, even mattered.

The debate came as lawyers moved forward with a multibillion-dollar settlement to resolve thousands of claims from women who blame implants for a variety of illnesses, including immune system disorders.

Dow Corning is among the companies that have signed the agreement, promising to pay women $2 billion over the next 30 years. Dow Corning denies implants hurt anyone.

The latest dispute centers around a 1975 study involving mice and D4, a purified form of silicone that is found in small amounts in implants.

Company spokeswoman Barbara Carmichael said the study found that D4 did not harm the immune systems of mice. Only when combined with a substance not found in implants did it have a temporary, minor effect on the animals, she said.

But an independent expert on silicone gel said the study showed that high levels of D4 were very toxic. In some cases, they killed the mice, said Dr. John Naim of Rochester (N.Y.) General Hospital.

In the study summary, Dow Corning scientists wrote that D4 decreased the disease-fighting ability of immune cells in mice.

Naim warned that the study does not necessarily translate to silicone gel implants, which contain lower levels of D4.

“Is it relevant? I don’t know,” he said. “Is it at a low enough level? That’s certainly a legitimate defense.”

The corporation, once the largest maker of silicone implants, told the U.S. Food and Drug Administration about the study last year, in one paragraph of a letter discussing a 1993 study that found a possible link between implants and immune system irregularities.

“This is not an effort to somehow hide stuff. We are interested in the public health and we are interested in discussing the science” behind implants, Carmichael said.

The FDA did not ask to see the 1975 study because Dow Corning’s characterization made “it not appear startling or significant,” spokesman Jim O’Hara said.

But implant opponent Dr. Sidney Wolfe of the Washington-based Public Citizen Health Research Group said the study uncovered alarming effects of D4 that are apparent in his reading of the company’s letter to FDA.

“FDA never asked Dow for the study, which is unconscionable,” said Wolfe, who lobbied the agency to ban implants. “This study really shows some things that haven’t been shown in previous studies. It is an important study.”

Carmichael said Dow Corning was not obligated to turn over the research because it was part of an effort to see if silicone could be used as a medicine and was unrelated to implants. The 1975 study was a follow-up to research done in 1974.

The FDA could not immediately say whether the study was legally required, because the Medical Devices Act governing such research was not passed until 1976. But O’Hara said the company should have disclosed the study in 1991, when the FDA held hearings on D4 and other components of implants.

Had the company released the study in 1975, Naim said, scientists might have launched objective research into the subject much earlier.

The 1975 study came to light as lawyers for women prepared to go to court against Dow Corning in the first federal trial involving breast implants.

The case had been set to begin this week in Birmingham, where U.S. District Judge Sam Pointer is presiding in more than 7,000 lawsuits combined into one. The trial was delayed after Dow Corning and two other companies signed a $3.7-billion settlement agreement.

Negotiations between the women’s lawyers and companies, including 3M and many other smaller companies, continue this week.

Stanley Chesley, a lawyer negotiating on behalf of the women, said lawyers on his side have known about the 1975 study for months.

Such documents, which companies were forced to release as evidence, are the main reason corporations such as Dow Corning agreed to the settlement, he said.

“There are documents against these manufacturers that are much worse,” Chesley said. “This is just the tip of the iceberg.”

Dow Corning contends that up to 1 million women have received implants, but the women’s lawyers say the number is closer to 650,000.