Dose, duration and mode of administration of hormones influence breast cancer risk

Majority of breast cancers are diagnosed in post-menopausal women. Hormone replacement therapy has been indicated as one of the major causes of increasing breast cancer risk in these women. Several epidemiological studies have attempted to discover the association between hormone replacement therapy and breast cancer. Because of the nature of data collection and study design it has been difficult to assess the real effect of hormone replacement therapy on breast cancer risk. Several hormones are biphasic in nature and one needs to take into account that the dose, duration and mode of administration of hormones could have a significant impact on increasing or decreasing the risk of breast cancer. This review will attempt to provide a broad summary of the evidence to date on the breast cancer risk associated with dose, duration and mode of administration of hormone replacement therapies.