Statistical Interaction In The Survival Analysis Of Early Breast Cancer Using Registry Data

Purpose: An interaction analysis is used to investigate subgroup effects between breast conserving surgery, radiotherapy and nodal status in early breast cancer. Patients and methods: Women selected from the SEER database, aged 40-69 with non metastasized T1-T2 breast cancer and in whom axillary node dissection was performed. The method uses proportional hazards regression models with interaction terms. Steps of the analysis are detailed. Results: Significant statistical interactions were found between breast conserving surgery, radiotherapy , nodal involvement and T stage. In an integrated factorial presentation of results, patients undergoing breast conserving surgery without radiotherapy were not at survival disadvantage as compared with patients undergoing mastectomy, irrespective of T-stage and irrespective of nodal involvement. However, the addition of radiotherapy to breast conserving surgery was associated with a distinct survival advantage observed in all T stage and all levels of nodal involvement. Conclusion: The analysis of interactions provides a comprehensive view of complex subgroup effects. The formal presentation of results might be useful as a framework to generate hypotheses for further investigations.