The findings, published in this week's issue of the British Medical Journal, suggest a double mastectomy may be an effective first-line treatment for women with early-stage breast cancer who carry a BRCA1 or BRCA2 genetic mutation.
Having a mutation in either of the BRCA genes leads to an elevated risk of breast and ovarian cancers. Certain ethnic groups, among them Ashkenazi Jews, have a higher prevalence of these genetic mutations.
"Women with a BRCA mutation have a 60 to 70 per cent chance of developing breast cancer in their lifetime and, once diagnosed, a further 34 per cent chance of developing breast cancer in the opposite breast within 15 years," said Kelly Metcalfe, a scientist at the Women's College Research Institute who led the study.
"For these women, we need to think about treating the first breast cancer, but also about preventing a second breast cancer."
To conduct the study, researchers analysed the medical records of 390 women with early-stage breast cancer and a BRCA1 or BRCA2 mutation.
Metcalfe said those who had both breasts removed had a 48 per cent greater likelihood of surviving compared to women with a single mastectomy.
The study also found that women who developed a new cancer in the opposite breast had double the risk of dying from the disease compared to those who had a double mastectomy.
At 20 years, the survival rate was 88 per cent for women who had both breasts removed and 66 per cent for women with a single breast removed.
To put it in more absolute terms, of the 79 women in the study who died of their cancer, 18 had undergone a double mastectomy and 61 chose to have only the cancerous breast removed.
"There are very few treatments that we can think about that would reduce a woman's risk of dying by this much," Metcalfe said.
"So ultimately, based on the results of this study, we think women should consider having a bilateral mastectomy as the treatment of their first breast cancer."
After being tested in 2000, Natalie Witkin of Toronto learned she had the BRCA1 mutation and had decided by 2007, at age 37, to have both breasts removed as a preventive measure. But 10 days before the operation, she was diagnosed with cancer in one of her breasts.
"Knowing I was a mutation carrier and I had a high risk of developing another breast cancer in either breast, I chose to have a double mastectomy," Witkin, now 45, said Tuesday. "Had I not known I was a BRCA mutation carrier, because I had an early-stage breast cancer, I most likely would have opted to have a lumpectomy.
"So I would say that this study shows that my decision to have a double mastectomy has likely improved my survival."
BRCA1-related breast cancer can be aggressive, making it more difficult to treat, especially if it is not caught early.
Last year, actress Angelina Jolie announced she had opted for a double mastectomy and breast reconstruction after discovering she carried the BRCA1 gene. The surgery was preventive — at the time, the then 37-year-old said doctors estimated she had an 87 per cent risk of developing breast cancer and a 50 per cent risk of ovarian cancer.
This study looked at women who had already been diagnosed with BRCA-related breast cancer to see which treatment conferred the greatest survival benefit over time.
"Our study's results provide evidence that in order to improve survival in women with BRCA-associated breast cancer, we need to prevent new breast cancers from developing after an initial diagnosis," said senior author Dr. Steven Narod, director of familial breast cancer research at Women's College Hospital.
"This study highlights the importance of providing genetic testing for BRCA1 and BRCA2 at the time of breast cancer diagnosis, if appropriate," he said. "This genetic information could help women make decisions that ultimately may increase their chance of surviving breast cancer."
BRCA testing is available in Canada to women who meet certain risk criteria, including their family history of breast cancer and ethnicity.
Metcalfe said women with a BRCA mutation who previously had breast cancer and had either a lumpectomy or a unilateral mastectomy may want to speak to their doctor about surgery to remove both breasts to reduce the risk of developing a new cancer — "and ultimately increasing their chance of survival."
In an accompanying editorial, Karin Michels, an associate professor of epidemiology at Harvard Medical School, said the decision to part with a healthy breast to "prevent a probability" is a difficult one to make.
While agreeing that the decision should be made with her doctor, Michels writes that "a woman needs to weigh up alternative options, including regular close monitoring and the use of (cancer-preventing drugs) tamoxifen or raloxifene, while considering the opportunities but also possible complications of reconstructive surgery."
"No statistics and no statistician can make this decision for her," said Michels, who suggested larger studies are needed to confirm the Toronto researchers' conclusions.
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