Tumor Stage Affects Risk and Prognosis of Contralateral Breast Cancer: Results From a Large Swedish-Population-Based Study

Purpose The number of breast cancer survivors at risk of developing contralateral breast cancer (CBC) is increasing. However, ambiguity remains regarding risk factors and prognosis for women with CBC. Patients and Methods In a cohort of 42,670 women with breast cancer in the Uppsala/Orebro and Stockholm regions in Sweden in 1992 to 2008, we assessed risk factors for and prognosis of metachronous CBC by using survival analysis. Breast cancer-specific survival for women with CBC was evaluated and compared with results for women with unilateral breast cancer (UBC) by using time-dependent Cox-regression modeling. Results An increased risk for CBC was observed among women who had primary breast cancer with >= 10 involved lymph nodes compared with node-negative women (adjusted hazard ratio [HR], 1.8; 95% CI, 1.2 to 2.7). The prognosis was poorer in women with CBC than with UBC. The hazard of dying from breast cancer was especially high for women with a short interval time to CBC (adjusted HR, 2.3; 95% CI, 1.8 to 2.8 for CBC diagnosed <= 5 years v UBC) and gradually decreased with longer follow-up time but remained higher than the hazard originating from the primary tumor for >= 10 years. Conclusion Women with advanced-stage primary breast cancer had an increased risk of developing CBC. CBC is associated with an increased risk of dying from breast cancer throughout a long period of follow-up after the primary tumor. Our findings suggest that the event of CBC marks a new clinical situation in terms of investigations for metastases, treatment considerations, and follow-up strategy. J Clin Oncol 30:3478-3485. (C) 2012 by American Society of Clinical Oncology