Association of Postoperative Radiotherapy Delay with Relapse and Metastasis in Women with Breast Cancer Using Penalized Cox Regression

Background: The impact of initiation time of radiotherapy after breast surgery on disease-free status of patient is a controversial issue. We assessed the relationship between the delay in adjuvant radiotherapy and surgery and relapse or metastasis- free survival in women with breast cancer taking heavy censoring into account. Method: This was a historical cohort study on 284 patients with breast cancer, who underwent surgery between 2001 and 2007 and followed up until March 2017. The association of the duration between radiotherapy and surgery, as well as other demographic and clinical factors with occurrence of local relapse or metastasis of breast cancer was examined through penalized Cox regression modeling. The obtained data were analyzed using R 3.6.3. Results: A total of 284 women with the mean age of 47.2 ± 11.3 years met the inclusion criteria. The maximum follow-up time was 11.1 years and the time between surgery and radiotherapy was 168 ± 84.3 days. About 10% of the patients experienced local relapse and 19% had metastasis. In multiple analysis of factors related to disease- free survival, the stage of disease was significant, while surgery to radiotherapy interval (≤180 days vs >180 days) did not have any significant impact on hazard of failure. Analysis of 3, 4, or 5 months of delay in radiation therapy did not imply any significant affects. Conclusion: In the studied patients, the delay in radiotherapy initiation after surgery did not lead into outcomes of local relapse or metastasis.