Breast Density Notification Legislation and Breast Cancer Stage at Diagnosis: Early Evidence from the SEER Registry

Abstract

Background: Twenty-eight states have passed breast density notification laws, which require physicians to inform women of a finding of dense breasts on mammography.

Objective: To evaluate changes in breast cancer stage at diagnosis after enactment of breast density notification legislation.

Design: Using a difference-in-differences analysis, we examined changes in stage at diagnosis among women with breast cancer in Connecticut, the first state to enact legislation, compared to changes among women in control states. We used data from the Surveillance, Epidemiology, and End Results Program (SEER) registry, 2005-2013.

Participants: Women ages 40-74 with breast cancer.

Intervention: Breast density notification legislation, enacted in Connecticut in October of 2009.

Main measure: Breast cancer stage at diagnosis.

Key results: Our study included 466,930 women, 25,592 of whom lived in Connecticut. Legislation was associated with a 1.38-percentage-point (95 % CI 0.12 to 2.63) increase in the proportion of women in Connecticut versus control states who had localized invasive cancer at the time of diagnosis, and a 1.12-percentage-point (95 % CI -2.21 to -0.08) decline in the proportion of women with ductal carcinoma in situ at diagnosis. Breast density notification legislation was not associated with a change in the proportion of women in Connecticut versus control states with regional-stage (-0.09 percentage points, 95 % CI -1.01 to 1.02) or metastatic disease (-0.24, 95 % CI -0.75 to 0.28). County-level analyses and analyses limited to women younger than 50 found no statistically significant associations.

Limitations: Single intervention state, limited follow-up, potential confounding from unobserved trends.

Conclusions: Breast density notification legislation in Connecticut was associated with a small increase in the proportion of women diagnosed with localized invasive breast cancer in individual-level but not county-level analyses. Whether this finding reflects potentially beneficial early detection or potentially harmful overdiagnosis is not known. Legislation was not associated with changes in regional or metastatic disease.

Keywords: breast cancer; cancer screening; health policy.

Figure 1

Stage at diagnosis among women in Connecticut and control states. Panel A depicts the distribution of stage at diagnosis among women ages 40–74 with breast cancer in control states. Panel B depicts the distribution of stage at diagnosis among women ages 40–74 with breast cancer in Connecticut. *Breast density notification legislation was enacted in October of 2009.

Figure 2

Age-adjusted breast cancer incidence by stage over time. The graph depicts age-adjusted stage-specific breast cancer incidence in Connecticut and control states from 2005 to 2013. The vertical bar represents the time of enactment of breast density notification legislation in Connecticut.