Determinants of stage at breast cancer diagnosis across different healthcare systems: an international multicentre cohort study.

BACKGROUND

Breast cancer stage at diagnosis varies across populations and healthcare settings. We aimed to identify factors independently associated with stage III disease across different healthcare contexts.

METHODS

We conducted a multicentre retrospective cohort study of patients with stage I-III invasive breast cancer diagnosed between January 1 and December 31, 2025, at four tertiary institutions in Spain, Costa Rica, Guatemala, and Panama. The primary outcome was stage III versus stage I-II disease. Multivariable logistic regression assessed age, country, molecular subtype, and diagnostic method. A sensitivity analysis replaced diagnostic method with routine screening. Model discrimination and calibration were assessed.

RESULTS

Among 918 patients initially identified, 843 were included; 632 (75.0%) had stage I-II and 211 (25.0%) stage III disease. Stage III prevalence ranged from 11.1% in Panama to 51.6% in Guatemala. Compared with Luminal A, Luminal B (adjusted OR [aOR], 2.28; 95% CI, 1.45-3.58), HER2-positive (non-luminal) (aOR, 4.01; 95% CI, 2.37-6.79), and triple-negative tumours (aOR, 1.91; 95% CI, 1.06-3.43) were associated with higher odds of stage III disease. Guatemala was also strongly associated with stage III presentation (aOR, 4.08; 95% CI, 2.68-6.20). Diagnostic method was not independently associated (aOR, 1.35; 95% CI, 0.94-1.94). In the sensitivity analysis (n=789), routine screening was not independently associated with stage III disease (aOR, 0.93; 95% CI, 0.64-1.35). The model showed an AUROC of 0.764 (95% CI, 0.733-0.806).

CONCLUSIONS

Stage III presentation was independently associated with molecular subtype and participating country/centre. Reducing advanced-stage disease may require integrated strategies addressing tumour biology, screening, timely diagnosis, and healthcare-system factors.