Early-stage breast cancer Personalized radiotherapy in breast-conserving treatment

Breast-conserving therapy (BCT) is standard treatment for early-stage breast cancer. Conventional BCT consists of a wide local excision followed by whole-breast radiotherapy. Adjuvant radiotherapy reduces the risk of a local recurrence (LR), but the benefit differs per patient.
The first part of this thesis focuses on local control after BCT and finding risk factors for LR. We studied 8507 patients treated between 1980 and 2008. The cumulative 5-and 10-year LR-rates were 2 and 5%, respectively. Young age was associated with a higher LR-risk, while the use of a radiotherapy boost and systemic therapy lowered the risk. Traditional clinicopathological factors are currently used to estimate the risk of LR. Additional biomarkers are needed to facilitate individualized treatment. Therefore, we investigated molecular risk factors for LR in young patients ≤ 50 years. Basal subtype was a strong risk factor for LR. We were unable to identify a genomic classifier for LR.
The second part of this thesis focuses on preoperative accelerated partial breast irradiation (PAPBI). For selected patients with low risk of LR, PAPBI is a promising treatment resulting in excellent cosmetic outcome and limited toxicity. Preoperative irradiation has several advantages, a.o. the possibility to study response to radiotherapy.
No significant differences in gene expression between patients with and without response to radiotherapy were identified. In addition, we investigated the ability of imaging modalities to predict pathological response. MRI was the most accurate method to predict response after preoperative radiotherapy. Larger studies will be required to identify reliably and clinically useful biomarkers.