The proportion of breast cancer patients who removed a healthy breast to prevent future cancers more than tripled over 10 years, but the procedure didn't improve their survival odds, a U.S. study finds.

Based on a decade of data on half a million women diagnosed with cancer in one breast that had not spread to other parts of the body, researchers found that removal of the second, healthy breast rose from 4 percent of patients in 2002 to nearly 13 percent in 2012.

But for women who chose so-called contralateral prophylactic mastectomy, the odds of death from breast cancer or from any cause were no different than those of women who just removed the tumor or the affected breast.

"It seems that what we're often doing is overtreating breast cancer," said senior author Dr. Mehra Golshan by email.

"Most women with early stage breast cancer will not benefit from having both breasts removed," said Golshan, the chair of surgical oncology at Brigham and Women's Hospital in Boston.

For the study, published in the Annals of Surgery, Golshan and colleagues analyzed a nationwide cancer database, focusing on 496,488 women diagnosed with stage I, II and III cancers in only one breast between 1998 and 2012.

They also looked at survival rates among more than 200,000 women through 2007.

Overall, around 60 percent of women underwent breast-conserving surgery, meaning removal of only the tumor, 33 percent removed only the diseased breast and 7 percent removed both breasts.

Nearly half of the women who had both breasts removed had reconstructive surgery, compared to 16 percent of women who removed one breast.

Golshan noted that while techniques are improving, surgery to remove breasts is still very serious. Operations can take between three and 12 hours, recovery can last a couple of months and women often lose most of the feeling in their chests.

He said that women may fear going through the experience of finding another lump in their other breast and not being able to work or sleep while waiting for test results.

Past research has found that anxiety and a lack of information about the risks and benefits can drive women to opt for preventive removal of a healthy breast (see Reuters Health story of April 22, 2015, here: http://reut.rs/22oMubV).

Dr. Monica Morrow, chief of the breast service at Memorial Sloan Kettering Cancer Center in New York, who was not involved in the study, also said that "having peace of mind" may motivate many women to choose to remove both breasts.

"Removal of the normal breast does nothing to reduce the risk of dying of the cancer that is already present, it simply reduces the risk of making a second cancer in the other breast (although it doesn't make the risk zero)," Morrow said.

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This risk of developing cancer in the opposite breast is very low for the vast majority of women, at around 0.5 percent chance, Golshan said.

He and his coauthors note in their report that even after adjusting for the subtype of cancer women had and other risk factors, there was no statistically significant difference in survival rates between women who had breast-conserving surgery and those who removed both breasts. But there was "slightly worse survival" among women who removed both breasts. There was not enough data to explain that pattern, however.

What has come to be known as the Angelina Jolie effect may be another factor in the trend toward removing both breasts, researchers noted. Publicity about celebrities who had genetic predispositions to cancer and preventively removed both breasts may have contributed to people believing that removal of both breasts is a "safer" approach, Morrow said.

"Women should talk to their doctors to find out what their actual risk of development of a second cancer is estimated to be before making this decision," she said.

"Surgeons should be operating less and we should have that discussion with the patient about the pros and cons of all the approaches," Golshan said.