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 metastasisfree survival in women with breast cancer taking heavy censoring into account. Method: This was a historical cohort study on ۲۸۴ patients with breast cancer, who underwent surgery between ۲۰۰۱ and ۲۰۰۷ and followed up until March ۲۰۱۷. 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 ۳.۶.۳. Results: A total of ۲۸۴ women with the mean age of ۴۷.۲ ± ۱۱.۳ years met the inclusion criteria. The maximum follow-up time was ۱۱.۱ years and the time between surgery and radiotherapy was ۱۶۸ ± ۸۴.۳ days. About ۱۰% of the patients experienced local relapse and ۱۹% had metastasis. In multiple analysis of factors related to diseasefree survival, the stage of disease was significant, while surgery to radiotherapy interval (≤۱۸۰ days vs >۱۸۰ days) did not have any significant impact on hazard of failure. Analysis of ۳, ۴, or ۵ 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.

Keywords:

Penalized Cox Regression , Breast Neoplasm , Radiotherapy delay , Local relapse , Metastasis