Adherence to guidelines and breast cancer patients survival: a population-based cohort study analyzed with a causal inference approach

Anita Andreano, Paola Rebora, Maria Grazia Valsecchi, Antonio Giampiero Russo

There is a lack of real-world studies evaluating the impact on survival of an evidence-based pathway of care in breast cancer. The aim of this work is to investigate the effect of adherence to guidelines on long-term survival for a cohort of Italian breast cancer patients. The cohort included incident female breast cancer cases (2007-12), from the registry of the Milan province (Italy), not metastatic at diagnosis and receiving primary surgery. We selected sets of indicators, according to patient and tumor characteristics. We then defined the pathway of care as adherent to guidelines if it fulfilled at least 80% of the indicators. Indicators were measured using different administrative health databases linked on a unique key. A causal inference approach was used, drawing a directed acyclic graph and fitting an inverse probability weighted marginal structural model, accounting for patient's demographic, socioeconomic and tumor characteristics. The analysis included 6333 patients, 69% of them were classified as having an adherent care. Mean age was 61 years (standard deviation, 13.6 years) and half of the patients were in Stage I (50%) at diagnosis. Median follow-up time was 5.6 years. Overall, 5-year survival was 90% (95% CI, 89-91%). The estimated risk of death was 30% lower for patients with adherent than nonadherent care (hazard ratio [HR], 0.66; 95% CI, 0.55-0.77). Our study confirms, in real-world care, the impact on survival of receiving a care pathway adherent to guidelines in non-metastatic breast cancer patients.