15 octobre, 2007 11:23

A message from Dr. Zuckerman on New Breast Implant Rupture Study and MRI's

When the FDA approved silicone breast implants in November 2006, the agency and the companies making implants warned women to undergo regular breast MRI screenings so that they would know if their implants were broken or leaking. The warnings tell women to get an MRI after 3 years, and every other year after that.

Breast MRIs are expensive -- averaging $2,000 -- and not covered by health insurance. Since the MRI warnings could discourage women from choosing silicone gel breast implants, it is not surprising that advertisements for breast implants do not mention MRIs, and many plastic surgeons have argued that MRIs are not necessary.

A new study published in Plastic and Reconstructive Surgery ("Magnetic Resonance Imaging and Explantation Investigation of Long-Term Silicone Gel Implant Integrity"-- see abstract below) concludes that silicone gel implants are unlikely to rupture until they are in the body at least 6 years, and that after 13 years only about 12% will be ruptured. The authors also conclude that MRIs are not necessary to check for rupture until 15 years, and only every 5 years after that. A careful review of the study shows that the plastic surgeons who wrote the article are basing their conclusions on wishful thinking rather than science.

Two of the authors are familiar names to experts on breast implants; Nick Collis and David Sharpe are authors of the "Sharpe/Collis" study that Mentor Corporation submitted to the FDA to prove the long-term safety of their silicone gel breast implants. The FDA scientists strongly criticized the Sharpe/Collis study, and their criticisms are also relevant to this study. In fact, it appears that this study is a slightly worse version of the study submitted to the FDA.

The first question for a thinking reader is: why is the rupture rate so much lower than the one reported by FDA scientists Dr. Lori Brown and her colleagues in 2001? Both studies were of women who had no idea that their implants might be ruptured. Brown et al found that most women in their study had at least one ruptured implant, whereas the new study by Colllis et al found that 14% had at least one ruptured implant.

There are two likely explanations for this difference, but Collis et al only focus on one: they believe that the implants in their study -- the kind of Mentor implants popular today -- are sturdier and last longer than the implants in the Brown study. They are probably correct -- BUT, that is not the most reasonable explanation for fewer ruptures. All the women in the Brown et al study had breast implants for at least 6-7 years and many had implants for more than 15 years; in the Collis study the minimum age of the implants was 4.8 years, and the maximum was only 13.5 years. Only one woman in the Collis study apparently had implants for over 13 years. The average age of implants was under 9 years.

Think of breast implants like a car tire. At first, most car tires are fine. Over time, they wear down. Those problems don't increase gradually from year 1 through year 20. The first few years are relatively trouble free, but the older your tires and the more you drive, the more likely the tires are to rupture. The increase in rupture is exponential after 50,000 miles -- and even more dramatic for any tires still on the road after 65,000 miles. You can't predict the percentage of tires that will go flat between 60,000-65,000 miles based on the percentage going flat between 10,000 and 15,000 miles. In the same way, you can't predict ruptures between 14-18 years based on the percentage ruptured between 6-10 years.

It's also important to remember that both the Brown study results and the Collis study results should be considered underestimates of rupture for a simple reason: both were "retrospective" studies that started at a time when women already had their implants for quite a few years and they eliminated any women whose implants had been removed before the study was started. In other words, any woman whose implant was removed in the first 4.5 years (and in many cases, even longer) was not eligible for the study. In fact, the Collis study used a database that was started in 1997, based on women who got implants since 1986 -- 11 years earlier. You'd think the women would therefore include many women who had implants for at least 11 years, but it doesn't. Why not? Since so few of the women in the Collis study had implants for 11 years or more, it seems that many of the women who had implants for a longer period of time were either ineligible for the study because their implants had been removed, or refused to participate (the refusal rate was about 50%. Whether the implants were removed because of pain, capsular contracture, or other reasons, it is likely that some of those removed implants were ruptured.

The Collis et al study tries to study one type of implant (Mentor's textured silicone implants) since 1986 and all were above the muscle. Therefore, the results are not relevant to implants placed below the muscle (which is more common in the U.S. today). In addition, the implants were relatively small, with approximately half 225 cc in size or smaller -- much smaller than the typical implant size in the U.S. today.

The bias of the Collis study interpretation is obvious in their published article. For example, the authors focus on the percentage of implants that are ruptured, not the percentage of women with ruptured implants. There is a big difference: since most women start out with one ruptured implant, the number of women with ruptured implants is almost twice as high as the percentage of implants that are ruptured.

That bias is also obvious in the authors review of previous studies. They don't even discuss the results of the Brown (FDA) study-- apparently, they don't like those results. They misquote a study of Holmich et al as finding a 15% rupture rate at 10 years, but actually what Holmich et al reported was a rupture rate of "at least 15%" -- and again that is 15% of implants but approximately 30% of women. (The Holmich study was funded by Dow Corning)

The most worrisome part of this published article is the conclusions, which are not based on data but rather wishful thinking. Even though less than a dozen women in the study had implants for 13 years or longer (the authors don't specify how many), the authors conclude that the rupture rate is 11.8% percent by 13 years. Even though none of the women in the Collis study had implants for 14 years or more, the authors conclude that MRIs are not necessary to check for rupture until the implants are 15 years old, and that MRIs are only needed every 5 years after that. But, obviously, all these implants could break in the 14th, 15th, and 16th year, and the plastic surgeons doing this study would have no way of knowing, since none of the women had implants that long.

Another important question about the study: if the women in the study started getting breast implants in 1986, why do none of the women have implants for more than 14 years when the study is published 21 years later?

What is also striking is how inaccurate the radiologists were at reading the breast MRIs in this study. FDA estimates that 86% of breast MRIs are accurate at determining rupture, but in this study the accuracy was approximately 67%.

Like most breast implant studies, this study is designed and interpreted in ways that reflect the financial interests of the funders and the authors. That's why we call them checkbook science . Most of these studies have been funded by Dow Corning or plastic surgeons. In this case, the study was conducted by plastic surgeons and partially funded by Mentor and also by a Plastic Surgery Department.

Diana Zuckerman, PhD