Purpose: Uncertainty remains about the impact of bilateral breast cancer. Characteristics and outcomes of unilateral and bilateral breast cancer were compared within an Australian multi-institutional cohort. Methods: Demographic, tumour and treatment characteristics were compared among unilateral (n = 2336) and bilateral cases (52 synchronous, 35 metachronous) using descriptive analyses. Disease-specific outcomes were investigated using Cox regression modelling to adjust for prognostic and treatment factors. Results: Factors associated with increased risk of bilateral breast cancer included lobular histology (p = 0.046), family history (p = 0.025) and metropolitan residence (p = 0.006). Mastectomy was more common for bilateral cases (p = 0.001) while radiotherapy was less common (p = 0.015). Index metachronous cases were less likely to receive hormonal therapy (p = 0.001). Five-year survivals for metachronous, synchronous and unilateral cases were 79%, 88% and 94%, respectively. Poorer outcomes remained after adjusting for prognostic factors [HR = 2.26, 1.21-4.21]. Conclusion: Our results confirm international findings indicating worse outcomes from bilateral compared with unilateral breast cancer.
- Breast neoplasm