CHICAGO (AP) - Breast implants in women who have undergone mastectomies often result in complications that require more surgery, a study in Denmark found.

Over a period of up to four years, about one-third developed at least one potentially serious complication, including thick, tight scarring and infections, the researchers reported. Implant ruptures were rare, with only five reported among the 574 Danish women studied.

Overall, about 20 percent of the women studied required surgery to treat the problems, according to the study by Danish Cancer Society researchers and scientists at the International Epidemiology Institute in Rockville, Md.

One surgeon said in an accompanying editorial that the numbers are "alarmingly high and arguably unacceptable."

The study appears in the December issue of Archives of Surgery. It was paid for by the institute, which receives funding from the Dow Corning Corp., a former maker of silicone breast implants.

Diana Zuckerman, president of the National Research Center for Women and Families, said the complication rate for implants in mastectomy patients is actually much higher than the study suggests.

Most participants got implants several weeks after breast removal surgery, whereas most U.S. mastectomy patients who choose implants get them when their breasts are removed, Zuckerman said. That method, involving a single round of surgery, is often easier psychologically because women wake up from their mastectomies with refashioned breasts, but it is also more stressful on the body, she said.

Also, she said the participants in the study did not undergo MRI scans, which are the best way to detect ruptures.

"This study is really missing the boat," said Zuckerman, whose group has opposed efforts to return silicone implants to the market.

All of the women studied got implants, most of them made of silicone.

Silicone implants have been restricted in the United States for over a decade because of fears that ruptures and leakage might damage women's health. But some mastectomy patients have continued to receive them.

The American Cancer Society estimates more than 200,000 U.S. women will be diagnosed with breast cancer this year. At least half will have mastectomies, and Zuckerman said about two-thirds of those patients choose some type of reconstructive surgery.

Many have breasts fashioned from excess flesh from their abdomens -- a method that is less likely than implants to result in thick scars and generally requires fewer "revisional" operations, said Dr. Navin Singh, a Johns Hopkins University surgeon and author of the accompanying editorial.

Singh said mastectomy patients are more prone to complications than healthy women seeking implants for purely cosmetic reasons, because much of their breast tissue and surrounding skin are removed during cancer surgery, giving doctors less to work with.

Also, some mastectomy patients may undergo radiation and chemotherapy, which can increase the risk of implant complications, he said.

Meredith Cobb, a hot line counselor for the Chicago-based breast cancer advocacy group Y-ME, said her silicone implants are not symmetrical and she needs more surgery to fix them. Still, the Colorado Springs, Colo., woman, who was diagnosed with breast cancer in 2003 at 26, said her implants have helped her "feel whole again."

"I wouldn't give them up now," she said. "A lot of people might not go through another surgery, but it's something that I'm willing to do," Cobb said.