The primary endpoints were AFR and LRR. AFR was defined as the first tumor recurrence, irrespective of LRR or DM. LRR was defined as any LRR as a first event with or without synchronous DM. Diagnosis of DM within 3 months of an LRR was considered synchronous. LRR occurring after DM was not considered as an LRR event. LRR indicated tumor recurrence in the ipsilateral chest wall; ipsilateral axillary, infraclavicular, internal mammary, or supraclavicular node recurrence; or a combination of these. DM indicated tumor recurrence outside regions identified as LRR sites. The secondary endpoints were DM and overall mortality. The information on date of death was taken from Korea's national database, in which death by breast cancer is not distinguished from death by other causes. Time to any recurrence or death was measured from the date of mastectomy.