Background/Objectives: Implementing organized, high-quality cancer screening programs in middle-income countries remains challenging, largely due to limited population coverage and gaps in quality assurance. This study assessed the performance of an organized breast cancer screening program under implementation in Brazil, using key performance indicators. This evaluation aims to inform the program optimization and support context-appropriate scalability across diverse sociodemographic settings.

Methods: Data from routine mammography and biopsy records within the Unified Health System were analyzed over a three-year period, encompassing the pre-implementation year (2023) and two years of the organized screening implementation (2024-2025). Mammography records were linked to biopsy registries to assess compliance with follow-up, time of diagnosis, and rates of true-positive and false-positive findings. Factors that may influence performance indicators were examined. The analysis encompasses data for women who underwent routine mammography screening in the state of São Paulo from January 1, 2023 to September 31, 2025. A total of 1,986,849 mammography exams were linked to 60,087 biopsies, totalizing 51,875 results.

Results: Comparing the pre-implementation year (2023) with the first year of ConeCta-SP regional workshops (2024), mammography screening coverage among the target population (women aged 50-74 years) increased in most Regional Health Departments (DRS). Coverage rose in different countryside regions, especially in Registro (24% to 37%). Greater São Paulo showed the highest coverage (53%), while a slight decline was observed in Presidente Prudente. Despite these gains, screening coverage in São Paulo remained below WHO recommendations. Although overall coverage did not increase substantially at the state level, diagnostic time improved in 2024, with a higher proportion of exams completed within 30 days. The proportion of inconclusive mammograms declined in several regions, though it remained above acceptable levels in Osasco and São João da Boa Vista. Follow-up compliance improved markedly (75.8% to 84.3%), false-positives decreased, and true-positives increased. Sociodemographic analyses showed a modest increase in screening among brown-skinned women and among women classified as high risk.

Conclusions/Recommendations: During the implementation of the ConeCta-SP strategies, breast cancer screening performance improved in key dimensions, particularly diagnostic time and follow-up compliance, despite persistently low coverage. These findings underscore the need for continued efforts to expand population coverage and reduce disparities.

Funding: FAPESP (2025/05545-2).