Population-based study results explain increasing CPM rates

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New results from a population-based study show that about 75% of women with cancer in one breast who chose to have a double mastectomy did so despite being at low risk of developing a new cancer in the unaffected breast. Greater degree of worry about cancer recurrence was associated with contralateral prophylactic mastectomy (CPM).

Only a small percentage of women diagnosed with breast cancer have clinical risk factors known to increase their chances of developing a new cancer in the unaffected breast. Those risk factors include mutations in the BRCA1 or BRCA2 genes, along with a strong family history of breast or ovarian cancer. Yet several studies, including a previous analysis of National Cancer Institute (NCI) SEER cancer registry data, show that rates of CPM among US women with breast cancer are increasing.

To investigate why women may choose CPM, investigators surveyed roughly 1,500 ethnically and racially diverse women diagnosed with breast cancer that had been reported to the Detroit and Los Angeles SEER registries. Of the 564 women who received mastectomies, 107 had CPM. The remaining women had breast-conserving surgery.

When the researchers compared survey responses in the two groups of women, they found that those who reported being “very worried” about recurrence were about twice as likely to have CPM as those who reported being “somewhat worried” or “not at all worried.”

In addition, women who reported having received positive test results for BRCA1 or BRCA2 mutations were about 10 times more likely to undergo CPM than those who did not have a mutation. Those with two or more first-degree relatives with breast cancer were about 4.5 times more likely to undergo CPM than those who did not have a strong family history of the disease. Although CPM reduces the risk of developing a new cancer in the unaffected breast for women with these clinical risk factors, the procedure has not been shown to reduce the risk of a recurrence of the original cancer.

“Our results suggest that many women are choosing a double mastectomy who really don't need it,” said Sarah Hawley, PhD, MPH, of the University of Michigan. “We want to make sure that women choose CPM with a good, clear understanding of what it's doing and not doing in terms of risks and benefits. What you do is a personal decision, but it should be an informed one.”

Hawley and her colleagues are still analyzing the survey data, so they have not yet examined some other possible reasons for why women may be opting for CPM.

These findings were presented on November 30, 2012, at the American Society of Clinical Oncology's Quality Care Symposium in San Diego.
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