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Hormone Replacement Lowers Sensitivity of Mammography

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Jan. 20, 2000 (Los Angeles) -- Women taking hormone-replacement therapy (HRT) may have less accurate results on mammography, researchers in Australia have found. The greatest impact was in women aged 50-69.

However, mammography still detected most of the breast cancers present, even in women on HRT, so these findings "should not deter a woman who's on HRT from going for screening," lead author Anne M. Kavanagh, BMBS, PhD, tells WebMD. Kavanagh is a senior research fellow at La Trobe University in Melbourne.

Kavanagh and her colleagues Heather Mitchell and Graham G. Giles studied more than 100,000 women participating in a regional mammography screening program in the Australian state of Victoria in 1994. The program, called BreastScan Victoria, provides free screening mammography every two years to all women 40 years old or more. The investigators compared the accuracy of mammography in women who were using HRT with that of women who were not on HRT. They determined how many women either had a tumor detected at the time of the initial mammography or were found to have cancer during the two-year interval between screenings. Of the women in this study, 27% were using HRT, mostly in the 50-59 age group.

Overall, nonusers of HRT developed 39 cancers in the first year after screening, compared with 23 cancers in users of HRT. Mammography sensitivity, which Kavanagh defines as "the capacity to detect cancer in women who will develop it within the next two years," was 12.5% lower in users than nonusers of HRT. Had the sensitivity been equivalent, the authors calculated that 23 more breast cancers would have been detected in the women on HRT, an increase of 20%. Sensitivity was lowest in the target age group, 50-69 years. Specificity, defined by Kavanagh as "the number of women who don't have cancer [on mammography] and who don't get called back for it," also was significantly lower in users of HRT.

Previous studies have similarly found a reduction in the sensitivity of screening mammography in the first year after screening in women on HRT, the authors write. Says Kavanagh, "It seems logical that HRT might decrease sensitivity because of its effect on the density of breast tissue." Younger women have denser breasts, she explains, and HRT makes a postmenopausal woman's breasts look "more like those of a premenopausal woman." This, in turn, makes mammography more difficult to read.

"Further research is needed to understand the impact of HRT on mammography," Kavanagh says. "We need to learn which types of HRT are most associated with increased breast density and decreased sensitivity." There is evidence that HRT-induced changes may be reversible, suggesting that simply by going off HRT for two weeks, a woman might have a more accurate mammogram. Once more information is available, the authors write, it "can then be used to advise women who use HRT about the appropriate approach to screening."

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