The American Women’s Health Initiative trial1 and large scale observational studies2 found that current use of menopausal hormone therapy (MHT) is associated with an increased risk of breast cancer, and that this risk is higher for combined oestrogen-progestagen therapy than for oestrogen-only therapy.
To obtain local and contemporary estimates for MHT associated breast cancer risk and to further quantify the risk by the type of hormonal preparation and duration of use.
We analysed data on 1106 self-reported incident breast cancer cases and 810 female self-reported cancer free controls from NSW CLEAR study, recruited between 2006 and 2013. Past and current MHT use was collected from all participants along with other lifestyle and demographic factors using a self-administered questionnaire. An unmatched multivariable logistic regression was performed, adjusting for socio-demographic, reproductive and lifestyle variables, BMI and breast screening.
The fully adjusted odds ratio (OR) for current users of any type of MHT compared to never users was 2.2(95% CI:1.6-3.0); whereas in past compared to never users it was 1.0(95%CI: 0.8-1.3) with no effect of time since last use. For current users of oestrogen-only and combined therapy the OR was 1.9(1.2-2.9) and 3.0(1.6-5.7) respectively. For both preparation types, adjusted ORs for breast cancer were generally higher in women who had used MHT for ≥10 years, compared to shorter duration users.
The findings from this Australian study are consistent with the findings from international studies that current, but not past, use of MHT is associated with increased risk of breast cancer and that this risk is higher in users of combined therapy.