If you are taking hormone replacement therapy (HRT), you should let your radiologist know about it every time you have your mammogram.

HRT can increase the density of the breast tissue and (because dense breast tissue shows up as white on a mammogram) make the breasts harder to evaluate on mammography. Unfortunately, cancers also look white on a mammogram, so the tumor polar bear may be hidden in that tissue snowstorm in your X-ray.

HRT can also make it more likely that abnormalities in your mammogram will result in a biopsy. It's unclear if HRT causes the abnormalities; however, a finding of densities in localized areas of the breast is likely to prompt a radiologist to do a biopsy to verify that the density is just fibrocystic tissue and nothing more worrisome. According to one recent study, about 1 in 10 women on HRT end up having a biopsy, a pretty significant percentage. And the percentage of women on HRT in whom abnormalities were found rose from 4 percent, after taking the medicine for 1 year, to 11 percent after 5 years.

So tell your radiologist if you are taking HRT. You don't want biopsies you don't need, and you certainly don't want to have an early cancer looking like a polar bear in a blizzard on your mammogram. It's also important to periodically reevaluate --ideally, every year -- whether you should still be taking the HRT. We know now that HRT should not be taken for the rest of one's life. Years ago, that was the practice, but it's no longer.