Effect of biennial mammography on stage at diagnosis and outcomes of breast cancer in the Brazilian public health system.

Abstract

e23371 Background: Breast cancer is the leading cause of cancer-related death among women in Brazil. Biennial mammography is recommended for women aged 50–69 years, but adherence to this screening interval in the Brazilian Unified Health System (SUS) remains low. We evaluated whether adherence to biennial screening is associated with stage at diagnosis and breast cancer mortality. Methods: Using the Nodian platform, which integrates open-source data from DATASUS, we conducted a retrospective analysis of outpatient records. Women diagnosed with breast cancer who had at least one mammography record prior to diagnosis between January 2008 and June 2025 were included. Patients were classified into three groups: adherent (regular biennial screening), prevention (mammography performed > 24 months before treatment initiation), and diagnostic (mammography performed ≤24 months before treatment, consistent with diagnostic evaluation). Outcomes were stage at diagnosis and breast cancer–related mortality during treatment. Odds ratios (OR) were calculated for late-stage disease (stages III–IV). Results: Among 27 million women who underwent mammography within SUS, 94,342 were diagnosed with breast cancer and had a prior mammography record. Only 10.2% adhered to the biennial screening protocol. Late-stage disease occurred in 36.4% of adherent women, compared with 43.1% in the prevention group and 47.2% in the diagnostic group. Non-adherence was associated with higher odds of advanced-stage diagnosis (prevention vs adherent: OR 1.33, 95% CI 1.26–1.39; diagnostic vs adherent: OR 1.58, 95% CI 1.51–1.65). A total of 2,066 breast cancer–related deaths were recorded (2.2%). Most deaths occurred in the diagnostic group (75%), followed by the prevention group (18%), while only 7% occurred among women adherent to biennial screening. Conclusions: Adherence to biennial mammography screening, observed in only a small proportion of the Brazilian population, was associated with earlier stage at breast cancer diagnosis and a markedly lower proportion of deaths. These findings indicate that maintaining regular screening intervals is more effective than isolated or symptom-driven mammography and should be a priority for breast cancer control strategies within the SUS.