Background: Controversy exists on the impact of bilaterality of breast cancer on survival. We used population-based data to compare survival of women with unilateral versus bilateral breast cancer.
Patients and methods: At the Geneva cancer registry, we identified all 7,912 women diagnosed with invasive breast cancer between 1970 and 2002. Breast cancers were categorized as unilateral, synchronous bilateral (contralateral tumour diagnosed within six months after the first tumour) and metachronous bilateral (contralateral tumour diagnosed over six months after the first tumour). With multivariate modelling we compared characteristics and survival between women with unilateral and bilateral disease.
Results: Patients with synchronous bilateral tumours (n = 155, 2.0%) had more often lobular histology and less frequently stage I disease than women with unilateral disease. Women with metachronous breast cancer (n = 219, 2.8%) received less often chemotherapy or hormone therapy for their first tumours. Ten-year disease-specific survival was similar (66%) after unilateral and metachronous bilateral breast cancer, but worse after synchronous bilateral cancer (51%). After adjustment, breast cancer mortality risks were not significantly increased for women with either synchronous or metachronous bilateral disease (Hazard ratios 1.1 (0.8-1.5) and 0.8 (0.5-1.4), respectively).
Conclusion: This large population-based study indicates that bilaterality of breast cancer is not associated with impaired survival.