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Magnitude of Second Contralateral Breast Cancer Risk Reduction with Bilateral Mastectomy in Breast Cancer Patients: Data from California, 1998-2015
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November 21 2019
Source: Cancer. 126(5):958-970
[PDF-181.34 KB]
Details:
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Alternative Title:Cancer
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Personal Author:
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Description:Background:
Increasingly, breast cancer patients undergo bilateral mastectomy (BLM). The magnitude of benefit is unknown.
Methods:
We used SEER data on all women diagnosed in California from 1998-2015 with stage 0-III unilateral breast cancer and treated with BLM versus breast conserving therapy including surgery and radiation (BCT) or unilateral mastectomy (ULM). We measured relative risks of second contralateral breast cancer (CBC) and breast cancer death using Fine and Gray multivariable regression modeling adjusted for the competing risk of death and death from another cause, respectively, and potential confounding factors. We measured absolute excess risk (AERs) of CBC as the observed minus expected number of breast cancers in the general population, divided by 10,000 person-years at risk.
Results:
Among 245,418 patients with median follow-up of 6.7 years, 7,784 (3.2%) developed CBC. Relative risks were lower after BLM (hazard ratio (HR) 0.10, 95% confidence interval 0.07-0.14) and higher after ULM (HR 1.07, 1.02-1.13) versus BCT. AERs were higher after BCT and ULM (5.0 and 13.6 more cases, respectively) than BLM (28.6 fewer cases). BLM reduced risk more for older women (38.0 fewer cases for age≥50, versus 17.9 among age<50) but provided similar risk reduction across categories of grade and tumor hormone receptor status. Compared to BCT, risk of breast cancer death was equivalent after BLM (HR 1.03, 0.96-1.11) and higher after ULM (HR 1.21, 1.17-1.25).
Conclusions:
BLM may reduce second breast cancer risk by 34-43 cases per 10,000 person-years compared to other surgical procedures but is not associated with lower risk of death. Second breast cancers are rare, and their reduction should be weighed against harms associated with BLM.
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Pubmed ID:31750934
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Pubmed Central ID:PMC7021576
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