When Veronica Contreras-Shannon learned five years ago that she needed a mastectomy for a stage 2 cancer in her right breast, she was sure she'd have her healthy breast removed too.

“I thought, ‘I can’t go through this again,’” she said.

Her doctors said they’d support her decision. But they also explained the risk of getting a new cancer in her left breast was very low. She changed her mind—and opted for a single mastectomy and reconstruction instead.

Contreras-Shannon is not alone: More women diagnosed with cancer in one breast consider getting their healthy breast removed, according to recent research. The practice is known as contralateral prophylactic mastectomy, or CPM.

In a study published last month, researchers with the American Cancer Society found that among women 20 to 44, the proportion choosing CPM rose to roughly 33 percent in 2012 from about 11 percent in 2004. For women 45 or older, the proportion choosing CPM increased to more than 10 percent in 2012 from just under 4 percent in 2004. Previous studies have shown that overall rates of CPM have been consistently on the rise since the late 1990s.  

Despite the growing popularity of CPM, for women with no other breast cancer risk factors, removing a healthy breast actually doesn't significantly reduce the risk of dying from breast cancer, according to the American Society of Breast Surgeons.

“Women with cancer in one breast substantially overestimate the risk of getting cancer in the other breast,” says Todd Tuttle, M.D., chief of surgical oncology at the University of Minnesota.

Risk estimates vary, but experts say the chances are only about 2 percent to 6 percent over 10 years that a woman diagnosed with cancer in one breast will develop a new cancer in her healthy breast.

Some women do have serious risk factors for breast cancer. For them, breast removal may be a reasonable decision, says Judy C. Boughey, M.D., professor of surgery at Mayo Clinic in Rochester, Minn. But removing a healthy breast may not substantially reduce the risk of developing a new cancer—even for those with a family history of breast cancer.

Here’s what you need to know if you’re considering a preventative mastectomy.

Know Your Risk Level

The American Society of Breast Surgeons and the National Comprehensive Cancer Network have recommended against prophylactic mastectomies for women with no other breast cancer risk factors.

Still, you may want to discuss the procedure with your doctor if you have any one of a few key risk factors:

History of chest radiation. Women with cancer in one breast who underwent chest radiation therapy before age 30 may be at a higher risk for a new cancer in the other breast, according to Boughey. This mainly applies to people who had another cancer early in life, such as Hodgkin's or non-Hodgkin's lymphoma.

Strong family history. Most women who get breast cancer—around 80 percent, according to the American Cancer Society—actually don’t have a family history of the disease.

However, women with cancer in one breast who also have a strong family history do have a higher risk of getting cancer in the other breast, says Boughey.

A strong family history is a first-degree relative who has also had breast cancer, such as a mother, sister, daughter, or brother, or two or more second-degree relatives (aunts/uncles, nieces/nephews, grandparents/grandchildren) on the same side of the family.  

One first-degree relative with cancer can raise your risk of getting a second cancer in your other breast to almost 9 percent for women between age 25 and 54, and to nearly 15 percent for women in their early 30s, according to one study in the Journal of Clinical Oncology.

Those numbers rise if a relative had bilateral breast cancer—cancer that appears in both breasts simultaneously.

Genetic risk factors. Scientists estimate only about 5 percent to 10 percent of breast cancer cases are caused by genetic mutations. That means it’s not necessary for every woman to have genetic testing.

But women with a strong family history of breast cancer or ovarian cancer should consider it, Tuttle says, to get a clearer sense of their risk. Consumer Reports’ Choosing Wisely Campaign also advises women to consider genetic testing if they have Ashkenazi Jewish heritage and a close family member who has had breast or ovarian cancer.

Mutations on certain genes, most notably BRCA1 and BRCA2, can significantly raise your risk of a new breast cancer in your second breast.

For women who’ve tested positive for BRCA1 or BRCA2 gene mutations, and who’ve had breast cancer in one breast, the risk of developing a new cancer in the second breast is between about 11 and 21 percent over 10 years. The risk of a new cancer rises as you age, and by age 70 it’s between 62 and 83 percent for this group.

A few other genetic mutations can also raise your risk of breast cancer, according to Steven Chen, M.D., president-elect of The American Society of Breast Surgeons and a surgical oncologist and breast surgeon in San Diego.

“A thorough family history done by your doctor or a genetic counselor may uncover these patterns and help guide the need for genetic testing or treatment,” Chen says.

The Risks of Removing Healthy Organs

Women considering removing a healthy breast should make sure their doctors discuss all the potential risks and benefits with them before proceeding.

Despite the prevalence of CPM, a study published this week in the Journal of Clinical Oncology found that many women still aren’t receiving appropriate guidance about their genetic risk. Those conversations are critical.

With a substantive discussion of the surgery—covering rates of survival, recurrence, development of a new cancer, as well as cosmetic outcomes and the recovery process—patients were more likely to be satisfied with their ultimate decision, found another study published this month in JAMA Surgery.

While people tend to carefully consider their risk of developing cancer in a healthy breast, they may not consider some of the risks associated with removing it. These risks include those associated with the surgery itself, such as bleeding and infection.

According to Tuttle, the complication rate after a single mastectomy with reconstruction is about 7 to 10 percent. It’s twice as high when a patient undergoes a double mastectomy and reconstruction.

If a woman opts for immediate breast reconstruction, an infection can mean losing the implant, Boughey says. And if a woman is planning on undergoing chemotherapy or radiation for cancer after a mastectomy, an infection in either surgical site can delay those treatments.

One of the hardest things to educate patients about is the numbness that comes with a breast reconstruction, Boughey adds. Even if the surgeon reconstructs a nipple, there can be no sensitivity or arousal.

“Women will tell you, it’s strange,” Boughey says. “‘I can hug you, but I can’t feel it when your body’s up against mine.’”

Why Some Women Choose Preventive Mastectomy

Despite the risks and downsides, many women still feel it's worthwhile to remove the healthy breast, says Atilla Soran, M.D., clinical professor of surgery at the University of Pittsburgh and a surgical oncologist at the Magee-Womens Hospital of UPMC.  

Soran has surveyed women who chose to have their healthy breast removed as well as the affected breast after a cancer diagnosis, and he found that almost all of them—97 percent, to be exact—were happy with their decision. Women cited fear of recurrence as the number one reason they chose CPM.

“Some of it is a sense of no regret,” Boughey says. They think, “‘If I were to fall in that 2 percent that had cancer in the other breast, I would never forgive myself.’”

For some women, it may be worth the risks of the surgery to alleviate the fear of a possible cancer in their other breast, Chen says.

“Patients feel that once they have breast cancer in one breast that they will be able to sleep better at night and have less anxiety if the other breast is removed,” says Boughey—even when a hard look at the numbers would suggest it’s an unnecessary intervention.

Other factors also played a role, Soran found. For instance, some said the fact that their insurance plans covered the surgery influenced their decision. It may be that some women who thought they might lose their insurance coverage later chose to remove a healthy breast partly in an attempt to avoid the costs of a potential second diagnosis and surgery later, according to Soran.

Others said discussions with friends, relatives, and spouses pushed them to go for it.

Finally, some women who have cancer in just one breast choose to remove and reconstruct both in order to achieve a more uniform appearance.

Your Risk, Your Choice

Although Contreras-Shannon has a family history of breast cancer, she learned through genetic testing that she doesn't carry a BRCA mutation that would raise her cancer risk. Her doctors put her personal risk of developing a new cancer in her healthy breast at just 3 to 5 percent.

For her, losing her healthy breast wasn’t worth the minimal risk reduction. “If I can be 50 percent operational,” she said, “I think I prefer that to no sensation whatsoever.”

Today, she says if she could go back, she’d make the same decision. Contreras-Shannon also says she’s met many women who’ve chosen CPM, who also say they’re happy with their choices—doing whatever they can to reduce their risk, even if the change is small.

No matter which way breast cancer patients are leaning, they should be sure to talk to their doctors to get a clear picture of their risk for a new cancer in the healthy breast—and the risks of an often unnecessary surgery.

“There’s always that worry,” acknowledges Contreras-Shannon. “I’m a scientist … probably compared to other people my understanding of what those risks mean is a little different.” But she understands that for most women, looking at the odds is not always convincing.