Changes in breast cancer risk distribution among Vermont women using screening mammography.

Background: Screening mammography utilization in Vermont has declined since 2009 during a time of changing screening guidelines and increased interest in personalized screening regimens. This study evaluates whether the breast cancer risk distribution of the state's screened population changed during the observed decline.

Methods: We examined the breast cancer risk distribution among screened women between 2001 and 2012 using data from the Vermont Breast Cancer Surveillance System. We estimated each screened woman's 5-year risk of breast cancer using the Breast Cancer Surveillance Consortium risk calculator. Annual screening counts by risk group were normalized and age-adjusted to the Vermont female population by direct standardization.

Results: The normalized rate of low-risk (5-year breast cancer risk of <1%) women screened increased 8.3% per year (95% confidence interval [CI] = 4.8 to 11.9) between 2003 and 2008 and then declined by -5.4% per year (95% CI = -8.1 to -2.6) until 2012. When stratified by age group, the rate of low-risk women screened declined -4.4% per year (95% CI = -8.8 to 0.1; not statistically significant) for ages 40 to 49 years and declined a statistically significant -7.1% per year (95% CI = -12.1 to -2.0) for ages 50 to 74 years during 2008 to 2012. These declines represented the bulk of overall decreases in screening after 2008, with rates for women categorized in higher risk levels generally exhibiting small annual changes.

Conclusions: The observed decline in women screened in Vermont in recent years is largely attributable to reductions in screening visits by women who are at low risk of developing breast cancer.