By Amy Norton
NEW YORK | Tue Aug 31, 2010 12:21pm EDT
(Reuters Health) – Hormone replacement therapy after menopause may interfere with the accuracy of mammograms used to screen for breast cancer — and the risk may be greater with hormones delivered by patch or injection compared with pills, a new study finds.
The findings, reported in the journal Menopause, add to the body of evidence that hormone replacement therapy (HRT) makes mammograms more difficult to interpret. And they also contradict the theory that HRT patches and injections might be less likely to cause problems than pills.
In addition, the study found that a newer type of hormone therapy used in some countries — a drug called tibolone, which has weak estrogen-like properties — seemed to affect mammogram accuracy just as much as conventional HRT did.
Using data from nearly 173,000 Danish women who underwent screening mammography between 1993 and 2007, researchers found that current hormone users were more likely to have a false-positive result than women who had never used HRT.
Of 39,104 women on HRT at the time of the mammogram, 602 — or about 1.5 percent — had a false-positive, meaning they turned out not to have cancer on further testing. That compared with 0.8 percent of the 133,638 women who had never used hormone therapy.
When the researchers looked at the various types of hormone therapy, they found that women using patches with combination estrogen-progesterone replacement, as well as those on injections of estrogen only, had about twice the false-positive risk of women using oral HRT.
Most women on HRT, regardless of the type, did not have a false-positive. Of the 529 women on estrogen-progesterone patches, for example, 16 had a false-positive.
And since this is the first study to find relatively greater risks associated with certain types of HRT, it is too soon to advise women to take oral forms in order to curb the chances of false-positive mammogram, according to the lead researcher on the work.