About 70% of women will undergo a double mastectomy following a breast cancer diagnosis despite a very low risk of developing cancer in the unaffected breast, a new study suggests.

New research from the University of Michigan Comprehensive Cancer Center in Ann Arbor shows that 90% of women who choose contralateral prophylactic mastectomy reported being very worried about the cancer recurring.

“Women appear to be using worry over cancer recurrence to choose contralateral prophylactic mastectomy. This does not make sense, because having a nonaffected breast removed will not reduce the risk of recurrence in the affected breast,” says Sarah Hawley, PhD, associate professor of internal medicine at the U-M Medical School, in a news release. The findings will be presented at the American Society of Clinical Oncology’s Quality Care Symposium in San Diego.

The study included 1,446 women who had been treated for breast cancer and had not had a recurrence. They found that 7% of women had surgery to remove both breasts. Among women who had a mastectomy, nearly 1 in 5 had a double mastectomy.

Women with a family history of two or more immediate family members with 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. But the same does not hold for women without these indications

“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,” Hawley says.

She and her colleagues have recently received a large grant from the National Cancer Institute that will in part allow them to develop a decision tool to help guide women through breast cancer treatment choices. “A decision tool like ours will solicit common misconceptions about breast cancer treatment and give women feedback to help them fully understand the options and risks involved,” she says.