The purpose of this trial is to investigate the difference in late radiation morbidity between partial breast irradiation and whole breast irradiation given to women operated on with breast conservation surgery for early breast cancer with a low risk of local recurrence.

The study is 2-armed. In both treatment arms the radiotherapy consists of 40 Gy in 15 fractions, 2.67 Gy per fraction. The primary endpoint in the trial is late radiation morbidity evaluated as fibrosis, secondary endpoints are other types of late morbidity, rate of local recurrence and an attempt to establish a genetic risk profile for development of late radiation morbidity.

The hypothesis is that women operated with breast conservation for a breast carcinoma with low risk of local recurrence can be offered partial breast irradiation without risking more late radiation morbidity compared to whole breast irradiation.

Inclusion Criteria:

• women 60 years or older
• operated for unilateral, unifocal early breast cancer pT1, pN0, M0, grade I or II, positive estrogen and/or progesterone receptor, HER2 negative

Exclusion Criteria:

• lobular carcinoma