HORMONE REPLACEMENT therapy (HRT) reduces the effectiveness of both mammograms and breast biopsies in accurately detecting breast cancer, research published this morning has found.
An analysis of the 16,600 post menopausal women who participated in the Women's Health Initiative (WHI) study suggests that more than one in 10 women taking combined HRT have abnormalities on mammography that would not be present if they were not on hormone therapy.
During the five-and-a-half year trial period, some 8,500 women were randomly assigned to receive standard HRT in the form of oestrogen combined with progestogen. A total of 8,100 women were given a placebo (dummy pill) over the same period. Each woman received a mammogram and a breast examination yearly; breast biopsies were performed where clinically indicated.
Dr Rowan Chlebowski and his colleagues concluded that "use of [ combined HRT] for approximately five years resulted in more than one in 10 and one in 25 women having otherwise avoidable mammogram abnormalities and breast biopsies, respectively, and compromised the diagnostic performance of both".
Another significant finding from the research, which was published in the Archives of Internal Medicine, was that the adverse effect of HRT on mammograms persisted for at least 12 months after stopping treatment. While it had been known that HRT increased the risk of breast cancer in post-menopausal women, this study is the first to show that taking oestrogen and progestogen means that women are more likely to have a suspicious looking mammogram.
HRT use significantly increases breast density; the authors suggest that this might be the mechanism behind the reduced accuracy of mammograms in women taking this therapy.
Anecdotal evidence had suggested that the negative effects of HRT on mammogram findings could be avoided by discontinuing hormone treatment a few weeks before, but this study disproves that.
"These findings represent a concern for post-menopausal women who are considering hormone therapy," Dr Chlebowski said. "They should take the results of this study into consideration and consult with their physicians before undergoing even short-term hormone therapy."
Today's research will add to the uncertainty surrounding mammography and breast cancer testing following last year's controversies in Portlaoise and Limerick. A review of mammography services at the Midland Regional Hospital showed that nine women who had previously been given the all-clear had, after all, got breast cancer.
The various controversies highlighted the fact that no test for breast cancer - mammogram, ultrasound or MRI scan - is 100 per cent accurate.
Last May, it emerged that Ms Rebecca O'Malley had her breast cancer diagnosis delayed for 14 months after a laboratory error was made at Cork University Hospital (CUH). The Health Information and Quality Authority (Hiqa) report into her care has been delayed and is not now expected to be made public until late March.