It can be devastating to be given a breast cancer diagnosis. Once the shock wears off, most patients want to do what they can to raise their odds of survival, torpedoing the chances they'll ever go through this again.

But a new study published in JAMA Oncology found that undergoing a double mastectomy -- a surgery where both breasts are removed -- doesn't increase the chances of survival after a breast cancer diagnosis, compared to having other common forms of surgery for the disease.

Doctors say this isn't entirely black and white, but it does raise a lot of questions about care for breast cancer patients. Here's what you need to know.

The study analyzed data from more than 661,000 women who were diagnosed with a range of breast cancers in one breast between 2000 and 2019. The researchers discovered that women who underwent a lumpectomy (where the tumor and surrounding tissue is removed but the breast is largely left intact) or a mastectomy (where one breast is fully removed) had a 7 percent chance of developing cancer later in the other breast.

But the researchers found that there was no survival advantage in having a double mastectomy. During the 20-year study period, 8.5 percent of women who had lumpectomies died from breast cancer, nine percent of women who had mastectomies died from the disease, and 8.5 percent of women who had double mastectomies died from breast cancer.

The researchers concluded that while having a double mastectomy is an "effective means" of preventing cancer, it "does not reduce the risk of dying of breast cancer."

"We were trying to get a better idea of how breast cancer behaves in a patient," lead study author Vasily Giannakeas, PhD, a researcher at the Women's College Hospital Research and Innovation Institute, tells Women's Health. "From a clinical perspective, we wanted to determine which surgical options improve survival in breast cancer patients."

Doctors say they're not shocked by the findings. "We've known this forever," says Janie Grumley, MD, a breast surgical oncologist and director of the Margie Petersen Breast Center at Providence Saint John's Center and Associate Professor of Surgery at Saint John's Cancer Institute in Santa Monica, California. "A lot of patients feel like they should have a bigger operation, but we've never seen a survival benefit from a bilateral mastectomy. Never, ever."

Brian Czerniecki, MD, a surgical oncologist at Moffitt Cancer Center, agrees. "For years, we have known that there is no survival benefit to bilateral mastectomy," he says. "Most do it for cosmetic or matching purposes."

Giannakeas agrees that his work is confirming what the medical community already knows. "Previous studies have shown that bilateral mastectomy does not reduce mortality from breast cancer," he says. "Our study is consistent with these findings."

Grumley stresses that the findings don't apply to women who have a genetic mutation that predisposes them to breast cancer, like a BRCA gene mutation. "Having a genetic predisposition puts you in a different category," she says. "But the average, run of the mill breast cancer patient does not have a genetic predisposition."

Since the study has received so much attention, Grumley says she's hopeful that it will help educate patients. "There is a myth that a bigger breast surgery is a better breast operation. We hear people all the time that say that," she says. "But there are bigger risks with a bigger operation. If you're not going to have that benefit, why would you do that?"