Contralateral prophylactic mastectomy showed a slight benefit for minority of breast cancers

Issue: September 25, 2008

ASCO Breast Cancer Symposium

WASHINGTON — A subset of women may obtain a small benefit from contralateral prophylactic mastectomy, but the results of a study conducted at M.D. Anderson Cancer Center showed that the procedure is unnecessary for the majority of women with breast cancer.

Isabelle Bedrosian, MD, an assistant professor of surgery at M.D. Anderson, presented the findings at the 2008 ASCO Breast Cancer Symposium.

Bedrosian said in an interview that the procedure only shows a benefit for women aged younger than 50 years with stage I-II ER-negative cancer. Even for those women, the benefit is small, she added.

“It is a small benefit in a small group of women. For many women, what our analysis shows is there is not the need to run out and get a double mastectomy,” she said. “The relative risk reduction in this group is 31%. I don’t have an absolute risk reduction, but it’s not going to be very large.”

The researchers evaluated the cases of 82,759 women with breast cancer and identified 6,478 women who had undergone contralateral prophylactic mastectomy.

A multivariate analysis showed the procedure was associated with disease-specific survival (P=.02).

The researchers found that the procedure was associated with a 31% relative reduction in disease-specific mortality in women aged 49 years and younger with stage I-II ER-negative cancer (HR=0.69; 95% CI, 0.49-0.96, P=.03). That reduction was associated with a decrease in contralateral breast cancer events for women who went through the procedure (0.18% vs. 1.11%, P=.035).

Young women with early-stage ER-positive disease had a low occurrence of contralateral breast cancer after undergoing a double mastectomy (0.29% vs. 0.18% in the ER-negative group), but women who did not have the procedure were equally unlikely to develop cancer again (0.60%). The researchers concluded that for women with ER-positive breast cancer, double mastectomy did not significantly increase the probability of contralateral breast cancer compared with women who did not undergo the procedure (0.29% vs. 0.60%, P=.15).

“If you take 100 women who had one breast cancer, the majority of them will never have another breast cancer event,” Bedrosian said. “Therefore, for most women, removal of the other breast was entirely unnecessary because they were never at risk for getting breast cancer.” – by Jason Harris

Patients are increasingly undergoing contralateral prophylactic mastectomy. In a study published in the Journal of Clinical Oncology in 2007, Tuttle et al found that contralateral mastectomy rates had risen from 1.8% to 4.5% by 2003, and in those who were undergoing unilateral mastectomy the rates were up to 11%. For the great majority of women, there will not be a survival benefit to this procedure. There may be a small group of women who do benefit. In Dr. Bedrosian's study, those with early-stage, ER-negative disease under age 50, may have a small benefit. However, even in this group the absolute benefit is very small. The reduction in risk of contralateral breast cancer was less than 1%, and breast cancer survival due to the procedure cannot exceed this number. Finally, genetic testing should be considered as this is the group of patients who will have the highest chance of having a BRCA1 mutation. We need to be careful about how we discuss this with patients.

– Susan M. Domchek, MD

Director of the Cancer Risk Evaluation Program
Abramson Cancer Center, University of Pennsylvania

For more information:

Bedrosian I. #2. Contralateral prophylactic mastectomy and survival. Presented at: 2008 ASCO Breast Cancer Symposium; Sept. 5-7, 2008; Washington.