Researchers at the University of Pennsylvania say some women with breast cancer may be overestimating the lifesaving potential of a preventive mastectomy.

A new study may give women better information as they weigh surgery options after diagnosis.

More American women are choosing preventive breast removal for their healthy breast, after learning about an original tumor. Profound anxiety about developing breast cancer in the opposite breast often motivates women, but researcher Robert Prosnitz and his team wanted to better understand the potential impact of a preventive mastectomy on life span and quality of life.

"The implication is that the patient views preventive opposite-side surgery as substantially reducing her chances of dying of breast cancer, many of them want to do "everything possible," and they are probably overestimating an adverse outcome from developing a cancer on the opposite breast," said Prosnitz, a radiation oncologist at the University of Pennsylvania.

Penn investigators calculated the risk for a breast cancer recurrence and weighed that against the possibility for a lower quality of life caused by surgery complications such as infection, loss of sensation, or body image changes.

Prosnitz says both long- and short-term side effects can reduce a woman's quality of life.

Using modeling software and established research on life expectancy, the team predicted the risks for women with an original early stage cancer.

For every 100 women who choose regular screening and close monitoring for their opposite side breast—instead of a preventive mastectomy—about 11 will die of breast cancer within 20 years. Just one of those women would die of an opposite-side breast cancer, Prosnitz said.

If you take the same group of 100 women and assume they do have the preventive surgery, 10 will die of breast cancer, he said. "Basically you are saving, kind of, one life out of a hundred by doing the opposite-side breast surgery," Prosnitz said.

The study only calculated risks for women with the usual chance for breast cancer, not for women with one of the gene variants that predispose them for cancer.

Steven Standiford is chief of surgery at Cancer Treatment Centers of America in Philadelphia.

"Sometimes someone's immediate reaction is, 'Just get them both off and get this all over with.' One of the important things this study says is that this may lower your risk a little bit, but the most important thing is to take care of the cancer. We can always do preventive work later," he said.

Standiford says his patients usually initiate the conversation about preventive surgery, especially women who have "bumpy, lumpy" breasts that are hard to screen, which makes it harder to detect a cancer.

"That's someone who may say to me, 'You know, I'm tired of all these mammograms, all these repeat studies, having all these biopsies, since we are having to take care of a cancer on one side, should we do something about the other side?'"

Standiford says those women have usually done lots of homework and soul searching, and he says that may better prepare them for surgery complications or body changes.