Background Women with unilateral breast cancer have an increased risk of developing bilateral breast cancer (BBC). Patients with metachronous BBC (mBBC) usually have an earlier age of onset, and their prognoses have been shown to be either similar or poorer than those with synchronous BBC (sBBC). Given the differing presentation and characteristics of breast cancers in the Asian population and the West, this study aims to characterize Asian patients with BBC. Methods All patients who had oncological breast surgery between 2001 and 2010 at the Singapore General Hospital and National Cancer Centre Singapore were reviewed. Patients with BBC were identified and studied. Results A total of 5520 Singaporean women had oncological breast surgery, 155 women (2.8%) had BBC. Of those with BBC, 47.1% (n = 73) were synchronous and 52.9% (n = 82) metachronous (mean interval of 39.4 months), and there was no difference in median age in both groups (54 years of age). Patients with sBBC were more likely to have a positive family history and had asymptomatic contralateral tumours. Although patients with sBBCs were more likely to have ER/PR positive and Her2 negative tumours, they had a lower 5-year overall survival than those with mBBC (P = 0.022). Conclusion Our study shows that Asian women with BBC have different characteristics to their Western counterparts. In particular, women with sBBC tended to have a lower 5-year overall survival compared to those with mBBC, despite having seemingly biologically favourable tumours, which suggest that there may be more underlying their tumour biology and genetics.
