Hormone replacement therapy alters sensitivity of screening mammography

Jan 25 - Screening mammograms are less accurate in women who use hormone replacement therapy than in nonusers, increasing the risks of both false-negative and false-positive results, results of a Australian study show.

If the findings are confirmed, information about how the accuracy of mammographic screening is influenced by HRT use may play an important role in helping women to determine whether or not to use HRT, Dr. Anne M. Kavanagh, of La Trobe University in Melbourne, Victoria, and colleagues explain in the January 22nd issue of The Lancet.

The investigators examined the effects of HRT on screening mammography sensitivity in the cases of 103,770 women, age 40 years and older, who underwent mammography through the BreastScreen Victoria program in 1994. They used the Victorian Cancer Registry to calculate the sensitivity, specificity and small-cancer detection rate over the next 2 years.

The sensitivity of screening mammography for the 2-year interval was only 64.8% in women using HRT, compared with 77.3% in nonusers, the researchers found. In the target group, women 50 to 69 years of age, sensitivity was 64.3% in women using HRT and 79.8% in nonusers.

Among women diagnosed with breast cancer during the 2-year interval, those using HRT were 60% more likely than others to have a false-negative result. Of women who were not diagnosed with cancer during the study, those taking HRT were 12% more likely than others to have a false-positive result.

"An additional 23 cancers, or 20% more cancers, would have been detected by screening among HRT users if the sensitivity of mammography was the same as for nonusers," Dr. Kavanagh and colleagues calculate.

The use of HRT is associated with increases in breast density, the team points out, and increases in breast density are linked to reduced sensitivity of screening mammography.

The next step in this research is to determine if some HRT formulations affect mammography results less than others, the researchers say. Further study is also needed, they add, to determine whether or not the effects of HRT on screening mammography results can be minimized by advising women to discontinue HRT for a short period before receiving a mammogram.

Lancet 2000;355:270-274.