Radiotherapy is one of the three modalities used in the primary treatment o
f breast cancer. For patients with ductal carcinoma in situ after complete
resection, adjuvant radiotherapy permits breast-sparing treatment and incre
ases the event-free survival. Radiotherapy is mandatory after breast-sparin
g excision of localized invasive carcinomas and reduces the rate of local r
ecurrence, albeit without affecting overall survival. Currently the data do
not permit identification of subgroups of patients with invasive breast ca
ncer after breast-sparing surgery in whom adjuvant radiotherapy could be de
clined. High-risk patients benefit from locoregional radiotherapy. Modern r
adiation techniques are no longer associated with cardiac morbidity and mor
tality. The optimal sequence of adjuvant radiotherapy and chemotherapy is u
nclear. Delayed radiotherapy is associated with an increased risk of local
recurrence whereas delayed chemotherapy is associated with an increased ris
k of distant recurrence.