A double mastectomy – the surgical removal of both breasts – may seem like the best way to prevent breast cancer from spreading, but new research suggests it has no effect on survival. 

A study led by the Women’s College Hospital Research and Innovation Institute in Canada found that for women diagnosed with cancer in one breast, the likelihood of survival is not increased by having the other breast removed as a preventative measure. Researchers found it reduced the risk of cancer occurring in the second breast by 88%, but mortality rates were the same because the cancer cells can spread to other parts of the body. 

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The study, published Thursday in JAMA Oncology, examined 108,084 breast cancer patients over a 20-year period. The risk of cancer developing in the second breast was 6.9% for those who had a singular mastectomy or lumpectomy – the removal of cancer from a breast – and 0.7% for those who underwent a double mastectomy. But death rates were nearly the same for all three rates: 16.7% for a single mastectomy, 16.3% for a lumpectomy and 16.7% for a double mastectomy. 

“That seems like a paradox,” researcher Steven Narod, of Women’s College Hospital, told STAT News. “If you get a contralateral breast cancer, your risk of dying goes up. But preventing it doesn’t improve your survival.”

Still, for women with the BRCA1 or BRCA2 gene variants, which significantly increase the risk of breast cancer, doctors stil recommend double mastectomies. The procedure also may reduce help anxiety among others.

But for other women, the study’s findings may serve as a reassurance of their options, experts said. 

“It suggests that there is absolutely no difference in survival if you have a lumpectomy, a mastectomy or a double mastectomy,” Dr. Eric Winer, director of the Yale Cancer Center, told the New York Times. 

Dr. Angela DeMichele, co-leader of the breast cancer program at Penn Medicine, told the newspaper that the study provided a rigorous analysis compared to previous studies with similar findings. Due to the possibility that breast cancer may spread elsewhere, surgery may not improve the likelihood of survival compared to other treatment options. 

“That is why chemotherapy and hormonal therapies are so important,” DeMichele said. “They are designed to kill these cells.”