Hormone replacement therapy and breast cancer

There is considerable evidence that the risk of breast cancer is related to ovarian function. However, the effect of postmenopausal hormone replacement therapy (HRT) on breast cancer risk continues to be debated in the absence of data from randomised controlled trials. Observational studies suggest that HRT probably promotes the growth of pre-existing breast cancers rather than initiating malignant transformation of breast epithelial cells but without exerting an obviously detrimental effect on disease-specific mortality. The controversy surrounding HRT and breast cancer has become additionally more complex as a result of the dilemma faced by clinicians advising women rendered oestrogen-deficient by breast cancer therapy. Whilst HRT is currently contra-indicated due to theoretical concerns that it will promote disease recurrence, its increasing, ad hoc prescription to symptomatic breast cancer patients has not been associated with an increase in disease recurrence. Large-scale randomised trials of HRT in healthy women and breast cancer survivors are now ongoing but it will be some years before useful clinical information becomes available. Until then, the limitations and biases implicit as a result of the design of observational studies must be borne in mind when interpreting such studies.