Survival From Synchronous Bilateral Breast Cancer: The Experience of Surgeons Participating in the Breast Audit of the Society of Breast Surgeons of Australia and New Zealand

Background: Previous studies generally indicate that synchronous bilateral breast cancers (SBBC) havean equivalent or moderately poorer survival compared with unilateral cases. The prognostic characteristics ofSBBC would be relevant when planning adjuvant therapies and follow-up medical surveillance. The frequency ofSBBC among early breast cancers in clinical settings in Australia and New Zealand was investigated, plus theirprognostic significance, using the Breast Cancer Audit Database of the Society of Breast Surgeons of Australiaand New Zealand, which covered an estimated 60% of early invasive lesions in those countries. Design: Rateratios (95% confidence limits) of SBBC were investigated among 35,370 female breast cancer cases by age ofwoman, histology type, grade, tumour diameter, nodal status, lymphatic/vascular invasion and oestrogen receptorstatus. Univariate and multivariable disease-specific survival analyses were undertaken.
Results: 2.3% of caseswere found to be SBBC (i.e., diagnoses occurring within 3 months). The figure increased from 1.4% in womenless than 40 years to 4.1% in those aged 80 years or more. Disease-specific survivals did not vary by SBBC status(p=0.206). After adjusting for age, histology type, diameter, grade, nodal status, lymphatic/vascular invasion, andoestrogen receptor status, the relative risk of breast cancer death for SBBC was 1.17 (95% CL: 0.91, 1.51). Afteradjusting for favourable prognostic factors more common in SBBC cases (i.e., histology type, grade, lymphatic/vascular invasion, and oestrogen receptor status), the relative risk of breast cancer death for SBBC was 1.42(95% CL: 1.10, 1.82). After adjusting for unfavourable prognostic factors more common in SBBC cases (i.e.,older age and large tumour diameter), the relative risk of breast cancer death for SBBC was 0.98 (95% CL:0.76, 1.26).
Conclusions: Results confirm previous findings of an equivalent or moderately poorer survival forSBBC but indicate that SBBC status is likely to be an important prognostic indicator for some cases.