This study provides evidence that hormone replacement therapy (HRT) may render mammographic screening less specific, and some but not all studies have reported reduced sensitivity of mammography in women who take HRT. Because women are increasingly turning to HRT, this study examined its effects on mammographic detection of breast cancer in 103,770 Australian women who were screened for the first time in 1994 and who at that time reported no personal history of breast cancer and had no breast lump or abnormal discharge. Screening was offered to women aged 40 years and older at 2-year intervals. Just more than one-fourth of women in the study population (27 percent) were using HRT at the time of screening. They were more likely to have other symptoms but less likely to have a strong family history of breast cancer than those not using HRT.
Screening for breast cancer was 12.5 percent less sensitive in HRT users than in nonusers. In the first year after screening, sensitivity values were 83.7 and 91.4 percent, respectively. For those aged 50 to 69 years, the target age group, the figures were 83.5 and 93.4 percent, respectively. Specificity also was significantly compromised in HRT users. Logistic regression analysis disclosed that, for women having cancer diagnosed during the 2-year screening interval, HRT users were more likely to have a false-negative result. Among those not given a diagnosis of cancer, the risk of a false-positive result was slightly greater for HRT users. In both HRT users and nonusers, small cancers (those measuring ≤10 mm in diameter) constituted 35 percent to 37 percent of all cancers in both HRT users and nonusers.
Screening mammography clearly was less sensitive in women using HRT than in nonusers in this study after adjusting for age, symptoms, and family history. Possibly users should be advised to stop for a brief time before being screened. Reports suggest that HRTrelated mammographic changes may be readily reversible. Hopefully additional work will show which formulations are associated with reduced mammographic sensitivity.