The New England Journal of Medicine has published the results of an analysis of the Women's Health Initiative (WHI) studies to review the association between hormone replacement therapy (HRT) and breast cancer. These results have been reported in the wider media (BBC).
The data from the original clinical trial reveals an increased risk of breast cancer in users of combination HRT (hazard ratio of 1.26) over 5.6 years. The majority of participants did not continue with HRT when this study was terminated in 2002. The increased risk was seen to rapidly decline during the 2 years of post-intervention follow up.
Data from the observational study group reveals an approximate doubling of breast cancer risk. Again this risk declined rapidly after 2002 when many participants stopped taking HRT medication.
It has been suggested that reduced uptake of mammography screening could also explain the differences in the observed cancer rates. This analysis found no differences in screening rates between the two groups.
The current BNF also notes the increased risk of breast cancer. Use of HRT for 5 years is associated with an additional 6 cases of breast cancer per 1,000 women for women aged 50 to 59 years old and an additional 9 cases in women aged 60 to 69 years old.
Action: Clinicians should already be aware of the increased risk of breast cancer associated with use of HRT. Patients may be reassured that this increase in risk declines rapidly after stopping treatment.
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