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Doctors "should be aware that breast cancer diagnosis is more difficult in women using combined hormone therapy," said lead researcher Dr Rowan T. Chlebowski. Such therapy has a considerable effect on the risks of having an otherwise avoidable mammogram or breast biopsy, he added.
Other studies have examined the impact of hormone replacement therapy on breast cancer detection, noted Chlebowski, a researcher with the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Centre in Torrance, California.
However, unlike the current study, these studies generally did not examine how hormone therapy affects breast cancer detection over the course of treatment, he explained. Because of this difference in study design, "we can provide, for the first time, precise estimates of what a woman can expect if she uses oestrogen plus progestin for about five years."
How the study was done
As reported in the Archives of Internal Medicine, the researchers analysed data from 16 608 postmenopausal women who were randomly assigned to receive oestrogen plus progestin or an inactive placebo as part of the WHI trial.
Mammography and breast examinations were performed at the start of the study and annually, and breast biopsies were performed according to the findings of these exams. The impact of hormone therapy on breast cancer detection was determined through 5.6 years of treatment.
Overall, 35 percent of mammograms in hormone users were considered abnormal compared with just 23 percent of those in placebo users. Most importantly, the mammograms performed in hormone users were less able to visualise breast cancer and resulted in more unnecessary biopsies.
'Patients should be made more aware of risk'
Stopping hormone therapy improved breast cancer detection with mammography and breast biopsy, but the diagnostic ability was still inferior compared with that in women who had never used oestrogen and progestin. The reduced ability to detect cancer persisted for at least 12 months after hormone therapy stopped.
Doctors should make their patients on combined hormone therapy aware that the risk of having an unnecessary mammogram or breast biopsy is "considerable," about 10 percent and four percent, respectively, over five years, Chlebowski noted. – (ReutersHealth) - February 2008
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