Time trends in breast cancer and menopause hormone therapy use in New Zealand

The publication of preliminary findings from the Women's Health Initiative (WHI) Study in 2002 suggested an increased risk of breast cancer among users of menopause hormone therapy (MHT). This resulted world-wide in a rapid and significant decline in the use of hormone therapy. It was later claimed that breast cancer incidence rates had fallen as a result of lower rates of hormone therapy use. Our aim was to investigate whether there was an association between changes in the use of hormone therapy and rates of breast cancer diagnosis in New Zealand subsequent to the publication of the WHI.

Validated prescription usage data along with breast cancer screening and cancer registration data were accessed. Time trends extending for 8 years after the publication of the WHI were assessed.

The use of hormone therapy for managing menopausal symptoms fell by about 70% following the controversy about its safety. Breast cancer registration rates among women aged 50-59 years had started to fall in advance of this change in prescribing. Changes in other age groups appear to coincide with changes in the screening eligibility for the national breast screening program rather than use of hormone therapy.

The time trend analysis does not support an association between changes in hormone therapy use and the incidence rate of breast cancer.