This study investigates risk factors and prognosis for developing contralateral breast cancer (CBC). This is a population-based study involving 42670 women diagnosed with breast cancer (1992-2008). Metachronous from synchronous CBC was distinguished using a 6 months interval. After exclusion mainly due to lack of data regarding follow-up, 37393 women were eligible for analysis. The median survival time for women is this study was 6.7 years, with incidence CBC rate of 3.5 per 1000 persons-years. The risk of CBC was almost twice as high with women who had more than 10 positive nodes versus women who were node negative. Extension of cancer to chest wall or skin (T4) more than doubled the risk also. Tumour grade and hormone receptor status was not associated with increased risk of CBC. Lobular histology increased risk (HR 1.3; CI 95% 1.1 to 1.6). Endocrine treatment reduced the risk of developing CBC. Multivariate analysis showed that women diagnosed with CBC within 5 years of initial diagnosis had significantly increased risk of dying from breast cancer, and endocrine therapy reduced the risk of women dying from CBC by one half. The risk of dying from CBC was significantly high for women with younger than 49 years old at initial diagnosis, and for women diagnosed with large CBC and/or positive nodes. The hazard of death was higher for CBC compared to UBC, and this risk did not decrease to the same level until 13 years after the initial diagnosis.
Journal of Clinical Oncology 2012, DOI: 10.1200/JCO.2011.39.3645
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