Women on hormone replacement therapy (HRT) are less likely to have their breast cancers detected by mammogram than other menopausal women, Australian research has found.
A five-year study of 1,557 women with breast cancer aged 55 or older found women on HRT had an increased risk of recording “false negatives” during routine mammograms.
Melbourne University epidemiologist Anne Kavanagh said 371 of the women, almost a quarter of the sample, were taking HRT, making their cancers easier to miss.
Associate Professor Kavanagh, the study’s chief investigator, estimated about 76 women – five per cent of the participants – had cancers not initially detected by mammogram because they were taking HRT.
“You’ll always find some women get their cancers missed whatever happens,” she said.
“For women on HRT, at the first round of mammography, 66 per cent of them got their cancers detected compared with 82 per cent of non-users.”
Prof Kavanagh, of the university’s Key Centre for Women’s Health in Society, said breast density the glandular tissue that appears white on a mammogram – was high in young women and in some of those women taking HRT, making tumours more difficult to detect.
Although this explained some of the false negative results, she said the researchers believed other unknown factors were also involved.
“For instance, it may be harder for us to get good images of the breast in women who are taking HRT because sometimes the breasts are more painful in these women,” Prof Kavanagh said.
The study involved women who attended BreastScreen Victoria for a mammogram during the mid-1990s.
Women were identified as either non-users or users of HRT although the study did not separate women by the different types of hormone replacement therapy used.
Prof Kavanagh said more research was needed before scientists could offer advice about whether women on HRT should be screened more frequently than the recommended every two years or whether ultrasound should be used in preference to mammograms.
Certainly, she said general practitioners should be advising women about the issues before a decision was made about going on HRT.
“This is just another bit of evidence GPs should be giving to women,” Prof Kavanagh said in an interview.
“We already know HRT increases your breast cancer risk but in addition to that, there’s also this problem of mammography not being able to pick up your cancers quite so easily.”
The study was published in the May issue of the journal, Cancer Epidemiology Biomarkers and Prevention.
Prof Kavanagh said because of the possibility of mammograms missing breast cancers, if women become aware of lumps and unusual changes between routine screens they should see their doctors.