Metachronous contralateral breast cancer: An analysis of risk factors and prognosis in 42,670 women in Sweden.

Abstract

1568 Background: The number of breast cancer survivors is rising and therefore the number of women at risk of developing contralateral breast cancer (CBC). We analysed the risk of and prognosis after CBC in relation to tumour characteristics. Methods: In a cohort of 42,670 women diagnosed with primary breast cancer in Uppsala/Örebro and Stockholm regions in Sweden between 01/01/1992 and 12/31/2008, factors associated with the risk of developing metachronous CBC were assessed using Cox proportional hazard modelling. We also evaluated breast cancer-specific survival for women with CBC in comparison to women with unilateral breast cancer (UBC), where characteristics of the contralateral tumour were entered as time-dependent covariates. Results: Women aged < 50 at the initial cancer diagnosis had the highest incidence of CBC. We observed an increased risk of CBC in women with increasing tumour size (p-trend < 0.05) and with ≥10 affected lymph nodes compared to node-negative cancer (adjusted HR 1.8, 95% CI 1.2-2.7). Lobular histology of the initial cancer also increased the risk of CBC (adjusted HR 1.3, 95% CI 1.1-1.6). Women with CBC had a worse prognosis than women with UBC, especially women with a short interval between the two cancers (adjusted HR 2.8, 95% CI 2.3-3.5 for CBC ≤5 years and HR 2.1, 95% CI 1.5-2.9 for CBC >5 years, compared to UBC). Increasing size of the contralateral tumour further increased the risk of dying from breast cancer (p-trend < 0.0001), as did affected lymph nodes (HR 4.6, 95% CI 3.4-6.2 vs. HR 2.1, 95% CI 1.6-2.6), high grade (p-trend < 0.001), lobular histology (HR 3.8, 95% CI 2.6-5.6 vs. HR 2.3, 95% CI 1.8-2.9 for ductal) and hormone receptor negativity (ER: HR 4.9, 95% CI 3.6-6.5 vs. HR 1.7, 95% CI 1.3-2.2; PR: HR 3.5, 95% CI 2.7-4.6 vs. HR 1.6, 95% CI 1.2-2.2). Conclusions: The influence of advanced stage of breast cancer on the risk of CBC together with a substantially poor prognosis for women in whom CBC occurred shortly after the initial cancer may imply that for some women CBC is a manifestation of active disease rather than a new primary. These findings indicate that surveillance and treatment plans may have to be adapted accordingly for women with a short interval between the initial and CBC.