Bilateral mastectomy significantly decreases the risk for a second contralateral breast cancer, but does not decrease the risk of death, compared with breast-conserving therapy, results of a large retrospective study indicate.
Among 245,418 patients followed for a median of 6.7 years, the risk of death from breast cancer was similar for those who had undergone either breast-conserving therapy or bilateral mastectomy (BLM) but was 20% higher among women who had undergone unilateral mastectomy (ULM) when compared with breast-conserving therapy, reported Allison W. Kurian, MD, MSc, from Stanford (Calif.) University, and colleagues.
“Second breast cancers are rare, and their reduction should be weighed against the harms associated with BLM,” they wrote in a study published online in Cancer.
The investigators extracted data from the Surveillance, Epidemiology, and End Results program on all women diagnosed with American Joint Committee on Cancer stage 0 to stage III unilateral breast cancer in California from 1998 to 2015 who were treated with either BLM versus breast-conserving therapy, including surgery and radiation or unilateral mastectomy.
They calculated the absolute excess risk of contralateral breast cancer as the observed minus expected number of breast cancers in the general population divided by 10,000 person-years at risk.
Of 421,643 women with a first diagnosis of primary breast cancer during the study period, 245,418 met the study criteria. Of this cohort, 7,784 (3.2%) developed a contralateral second breast cancer more than 6 months after diagnosis of the first, after a median 6.7 years of follow-up.
Slightly more than half of the cohort (52.1%) had undergone breast-conserving therapy, 37.5% underwent unilateral mastectomy, and 7.6% had bilateral mastectomy. An additional 2.9% of patients were women aged 70 years and older with stage I hormone receptor–positive, HER2-negative disease who underwent breast-conserving surgery without radiation (percentages exceed 100% because of rounding).
A multivariate-adjusted model showed that, as might be expected, patients who underwent bilateral mastectomy had a 90% reduction in risk of contralateral cancer (hazard ratio, 0.10; P less than .001), compared with breast-conserving therapy. In contrast, patients who underwent unilateral mastectomy had a slight but significant increase in risk for a second contralateral breast cancer (HR, 1.07; P = .008).
The absolute excess risk for second contralateral breast cancer was 5 per 10,000 person-years with breast-conserving therapy, 13.6 per 10,000 person-years with unilateral mastectomy, and –28.6 per 10,000 person-years with bilateral mastectomy.
When they looked at risk for death, however they found that, compared with breast-conserving therapy, breast-conserving surgery alone (HR, 1.36; P = .0001) and unilateral mastectomy (HR, 1.21; P less than .001), but not bilateral mastectomy (HR, 1.03; P = .35) were significantly associated with increased risk for breast cancer death.
The authors noted that their estimates of absolute risk of second contralateral breast cancer jibe with those of earlier studies, and can help clinicians frame the discussion of the benefits versus risks for individual patients.
“What one patient might consider to be a negligible benefit of BLM, weighed against its potential harms of greater pain, recovery time, and impact on body image and employment, might appear worthwhile to another,” they wrote.
The study was funded by the National Cancer Institute, National Institutes of Health, Department of Health & Human Services, Suzanne Pride Bryan Fund for Breast Cancer Research, Jan Weimer Faculty Chair for Breast Oncology, and the BRCA Foundation. Dr. Kurian disclosed institutional research funding from Myriad Genetics.
SOURCE: Kurin AW et al. Cancer. 2019 Nov 21. doi: 10.1002/cncr.32618.