Omission of radiotherapy after breast-conserving surgery: survival impact and time trends.

Purpose: To evaluate the survival impact of omission of radiotherapy after breast-conserving surgery and the changes with time.

Material And Methods: Women aged 40-69 with non-metastasized T1-T2 breast cancer, who underwent breast-conserving surgery with axillary node dissection, with or without post-surgery radiotherapy, selected from the SEER (Surveillance, Epidemiology, and End Results) database. The analysis uses proportional hazards models.

Results: Omission of radiotherapy as compared to delivery of radiotherapy was associated with an overall increased mortality hazard ratio of 1.346 (95% confidence interval: 1.204-1.504). Test of constancy showed significant changes with time. The time profile suggested an exponential-like increase from a baseline mortality hazard ratio of 1.17, or 17% excess of relative mortality risk, to a projected hazard ratio of 2.26, or more than doubling of relative mortality risk, for omission of radiotherapy.

Conclusion: Omission of radiotherapy in breast-conserving surgery is found to be independently associated with an increase in mortality. The data do not give support to omitting radiation or give rationale to clinical trials that would omit radiation.