Breast cancer adjuvant radiotherapy - when can it be omitted?

The aim of adjuvant radiotherapy in patients with breast cancer is to reduce the risk of disease recurrence; both local and systemic. It also contributes to better overall survival. However, that effect is not consistent across all subgroups of patients. Bearing in mind radiotherapy’s side effects, it is crucial to define patients in which radiotherapy effect on the control of the disease is so low that it can be safely omitted. In general, those would be patients age 70 years or older after breast conserving surgery with hormonal receptor positive tumors, which are smaller than 2 cm (T1) and with uninvolved axillary lymph nodes (N0). It is a matter of discussion whether the same can be applied on HER2 + tumors, on tumors size up to 3 or even 4 cm, or in patients older than 65 or even older than 60 years. Upon mastectomy, radiation should be omitted in patients with tumors lesser than 5 cm and with uninvolved lymph nodes (pT1-2N0 stage). In case cancer treatment started with neoadjuvant systemic therapy, radiotherapy is always indicated after breast conserving surgery, but after mastectomy in clinically or patohistologicaly positive lymph nodes (tumor stage cN+ or ypN+). Pathological response of the tumor on given systemic treatment should not be the major factor determining the decision about indication for radiotherapy.