The performance of mobile screening units in a breast cancer screening program in Brazil.

Abstract

In Brazil, access to breast cancer screening outside of urban centers is limited. This study aims to describe the coverage and performance of a breast cancer screening program implemented with Mobile Screening Units (MSU) in northern São Paulo state. This is a retrospective cohort study of a population-based mammography program targeting women ages 40-69 in 108 municipalities from 12/2010 to 07/2015. Screening coverage rates were estimated using the Brazil 2010 census data. We calculated performance measures for the number of exams, recalls, and detected cases of cancer. Screen-detected cases were compared to clinically detected cases using hospital cancer registry data and a propensity-score matching method. The down-staging of screen-detected cases relative to clinically detected cases was assessed using logistic regression to calculate risk ratios (RRs) with 95% confidence intervals. 122,634 women were screened through the MSU program, representing a cumulative coverage rate of 54.8% in the target population. For initial and subsequent rounds, recall rates were 12.25 and 6.10% and cancer detection rates were 3.63 (95% CI 3.23-4.10) and 1.94 (95% CI 1.59-2.41), respectively. 92.51% of referrals were successful. Screen-detected cases had more favorable prognoses than clinically detected cases, including smaller tumor size and a decreased risk of late-stage detection (RR 0.14 95% CI 0.074-0.25). MSUs are a feasible method for the delivery of mammography services in this setting. Patients who had breast cancer detected on an MSU had favorable prognostic factors when compared with clinically detected cases arising from the same target population.