Vasomotor menopausal symptoms are not associated with incidence of breast cancer in a population-based cohort of mid-aged women

Background: Recently, two case-control studies showed that vasomotor menopausal symptoms (VMS), i.e. hot flushes (HF) and night sweats (NS), are associated with a decreased risk of breast cancer. Until now, however, no prior studies have prospectively examined the association between VMS and breast cancer incidence. We investigated this in a population-based cohort of mid-aged women in Australia. Methods: We included 11,297 women without a history of breast cancer aged 47–52 years from the Australian Longitudinal Study on Women’s Health, surveyed every 3 years from 1998 to 2010. Information regarding first invasive breast cancer events and date of diagnosis was obtained from cancer registries. We determined the association between HF and NS and breast cancer occurrence before the subsequent survey, using time-dependent cox regression analysis, adjusting for time-varying lifestyle factors. Results: At baseline 33.1% of the women reported experiencing HF and 24.6% reported NS. During a mean follow-up of 13.7 years, 348 cases of breast cancer occurred. VMS were not associated with breast cancer; adjusted hazard ratios were 1.09; 95% confidence interval (CI) 0.87–1.35 for HF and 1.06; 95% CI 0.84–1.33 for NS. No significant interactions were found between each of body mass index, alcohol use, current hormone therapy use, menopausal status and VMS and breast cancer (p-values > 0.05). Conclusions: We did not find an association between VMS and breast cancer incidence. Research in this area is scarce and additional large prospective population-based studies are required to confirm or refute these findings.