Four RCTs (n=3,665) were included in the review. Sample size ranged from 818 to 1,046. All included trials were high quality (Jadad score of 4). Median follow-up of included studies ranged from four to twelve years.
Compared with observation alone following breast conserving surgery, adjuvant radiotherapy was associated with a significant reduction in ipsilateral ductal carcinoma in situ recurrence (OR 0.40, 95% CI 0.31 to 0.53; four RCTs) and ipsilateral invasive breast cancer recurrence (OR 0.40, 95% CI 0.33 to 0.60; four RCTs), but with a significant increase in contralateral breast cancer recurrence (OR 1.53, 95% CI 1.05 to 2.24; four RCTs). There was no significant difference in overall mortality and distant metastasis rate between the two groups.
Significant heterogeneity was only observed in the outcome of ipsilateral ductal carcinoma in situ recurrence (I2=69.2%). Little evidence of publication bias was found.