Screening mammography intervals among postmenopausal hormone therapy users and nonusers

Abstract

The recent decline in US breast cancer incidence rates has been attributed to the marked reduction in use of postmenopausal hormone therapy (HT). An alternative explanation is that women who are not routinely seeking medical care to renew HT prescriptions may be less adherent to recommendations for mammographic screening. To investigate the latter possibility, we compared mammographic intervals according to HT use. Using data (1995-2007) from the New Hampshire Mammography Network (NHMN), a state-based mammography registry, we assessed mammographic intervals corresponding to HT use or nonuse among postmenopausal women. We used linear mixed effects models to assess whether the length of screening mammogram intervals differed according to HT use. A total of 310,185 mammograms, representing 76,192 postmenopausal women and 319,353 person-years of screening, were included in the analysis. The median screening interval corresponding to HT use overall was 13.0 months (interquartile range: 12.4-15.1) and for nonuse was 13.1 (interquartile range: 12.4-15.8). Virtually, all screening mammograms occurred within a 2-year interval regardless of HT use or nonuse (98.5 and 98.1%, respectively). Our findings indicate that screening mammography intervals are similar whether or not women are using HT. Thus, reduced utilization of screening mammography is unlikely to account for the decrease in breast cancer incidence seen soon after the WHI report.