The influence of socioeconomic status and ethnicity on adjuvant systemic treatment guideline adherence for early-stage breast cancer in the Netherlands

Background: We aimed to assess whether socio-economic status (SES) and ethnicity affect adjuvant systemic therapy (AST) guideline adherence in early breast cancer patients in a health care setting with assumed equal access to care. Methods: Data from all female patients surgically treated for primary unifocal early breast cancer between January 2005 and December 2014 were retrieved from the Netherlands Cancer Registry. We assessed the association between SES, ethnicity and non-adherence to adjuvant chemotherapy (CT) or endocrine therapy (ET) guideline indications with Poisson regression models, adjusting for clinicopathological variables. Results: 104,201 patients were included in the current analysis. Of patients without an indication, 4% and 13% received adjuvant CT or ET ("overtreatment"), whereas 39% and 14% of patients with an indication did not receive CT or ET ("undertreatment"). Medium and low SES patients were 1.01 (95%CI 1.00-1.01) and 1.01 (95%CI 1.00-1.01) times more likely to be undertreated and 0.85 (95%CI 0.76-0.94) and 0.67 (95%CI 0.60-0.75) times more likely to be overtreated with CT compared to high SES patients (resulting in an overall relative risk of CT use of 0.94 (95%CI 0.92-0.96) and 0.85 (95%CI 0.83-0.87), respectively). No association between SES and ET guideline adherence or ethnicity and CT/ET guideline adherence was observed. Conclusion: in the Netherlands, minimal SES disparities in CT guideline adherence were observed: low SES patients are less likely be overtreated and marginally more likely to be undertreated with CT resulting in an overall decreased risk of receiving CT. No ethnical disparities in AST guideline adherence were observed.