A new study finds the majority of women who have both breasts removed after a breast cancer diagnosis had a very low risk of developing cancer in their healthy breast, raising the question of whether there is the potential for overtreatment in these types of patients.

Many women who are diagnosed with breast cancer decide to have both of their breasts removed, a procedure known as double mastectomy (or contralateral prophylactic mastectomy). Now a new study, published in JAMA Surgery, finds that although fear about recurrence was a factor affecting their decision, 70 percent of those women who had both breasts removed had a very low risk of developing cancer in their healthy breasts.

The researchers from the University of Michigan Comprehensive Cancer Center studied 1,447 women who had been treated for breast cancer and who had not had a recurrence. The study found that 8 percent of women had a double mastectomy, and that 18 percent considered having one.

According to the American Cancer Society, 235,030 Americans will be diagnosed with breast cancer this year, and 40,430 will die from the disease.

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According to recent studies, women with breast cancer have been increasingly choosing to have this aggressive surgery because they are worried about recurrence. About three-quarters of patients reported being very worried about their cancer recurring.

But a diagnosis of cancer in one breast does not increase the likelihood of cancer recurring in the other breast for most women, according to the researchers.

Lead study author Sarah Hawley, Ph.D., associate professor of internal medicine at the University of Michigan Medical School, said in a press statement that women appear to be using worry over cancer recurrence to choose contralateral prophylactic mastectomy, “This does not make sense, because having a non-affected breast removed will not reduce the risk of recurrence in the affected breast,” said Hawley.

Dr. Elisa Port, chief of breast surgery and director of the Dubin Breast Center at The Mount Sinai Hospital in New York, told Healthline, “When women have breast cancer in one side, they do tend to overestimate their risk of getting a new cancer on the other side. It is our job, as surgeons, to provide accurate information regarding these risks so women can make decisions based on knowledge, and not driven by fear. Importantly, breast cancer can come back or recur after someone’s been treated and cured. But usually it does not come back in the other breast. For women with breast cancer, the decision whether or not to remove the other healthy breast has to be done on an individual basis, and should be a decision made by the individual woman with guidance from her surgeon.”

The study also found that women with higher education levels and women who had undergone an MRI test before surgery were more likely to choose double mastectomy. Concern about recurrence was one of the biggest factors driving the decision to have this surgery.

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The researchers asked study participants about the type of treatment they had, as well as the clinical indications for double mastectomy, including the patients’ family history of breast and ovarian cancer, and the results of any genetic testing.

Women with a family history of breast or ovarian cancer, or with a positive genetic test for mutations in the BRCA1 or BRCA2 genes, may be advised to consider having both breasts removed, because they are at high risk of a new cancer developing in the other breast. This represents about 10 percent of all women diagnosed with breast cancer. Women without these indications are very unlikely to develop a second cancer in the healthy breast, according to the researchers.

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The study found that among women who had a double mastectomy, nearly 70 percent did not have either a family history or positive genetic test. Many of these women were candidates for breast-conserving lumpectomy.

“For women who do not have a strong family history or a genetic finding, we would argue it’s probably not appropriate to get the unaffected breast removed,” said Hawley, in the press statement.

A double mastectomy may result in more complications and a more difficult recovery. In addition, most women went on to have breast reconstruction as well, and may also need chemotherapy or radiation therapy after their surgery, which the researchers said could further delay their recovery.

The researchers suggest there is a need for more education among women about the risks and benefits of contralateral prophylactic mastectomy. Surgeons should also be aware that patients’ treatment decisions are affected by their worry about recurrence, said the researchers.