Potential risk factors for local breast cancer recurrence after mastectomy in the Netherlands : a retrospective nationwide cohort study

Objective: Despite the supposed complete removal of glandular breast tissue in mastectomy, breast cancer patients still experience local recurrence after the surgery. Moreover, limited research currently exists on isolated local recurrence as opposed to locoregional recurrence of breast cancer after mastectomy. This study aims to identify potential risk factors associated with the development of local breast cancer recurrence after mastectomy. Methods: Based on data from the Netherlands Cancer Registry, a retrospective nationwide cohort study was conducted on women diagnosed with primary invasive nonmetastatic breast cancer between 2012 and 2016 and treated with mastectomy. Potentially relevant variables were selected based on univariable Cox regression before inclusion in multivariable cause-specific Cox regression to estimate the hazard ratios for local recurrence. Separate models were constructed for patients with and without neoadjuvant systemic therapy. Collinearity was assessed using variance inflation factors and interaction variables for potentially collinear variables. The goodness of fit was visually assessed using the Cox-Snell residuals. Multiple imputation was used to account for missing data. Results: In total, 22,304 patients were selected, of which 17,250 patients were included in the nonNST group and 5,054 patients in the NST group. In the non-NST group, statistically significant associations with local recurrence were found for menopausal status, socioeconomic status, screening detection, sublocalisation, differentiation grade, pathologic tumour and nodal stages, immediate breast reconstruction, hormone receptor status and treatment, HER2 status and treatment, radiotherapy type, and chemotherapy. For the NST group, statistically significant associations with local recurrence were found for clinical tumour stage, pathologic complete response, presence of a DCIS component, HER2 status, hormone receptor status and treatment, and radiotherapy type. No collinearity between variables was detected and all models showed adequate goodness of fit. Conclusion: The study results indicate potential risk factors for local recurrence after mastectomy. Further investigation of these variables is essential for improving the outcomes of breast cancer patients by optimizing post-surgical care based on individual patient, tumour and treatment characteristics.