Intact Mre11/Rad50/Nbs1 complex predicts good response to radiotherapy in early breast cancer

• Purpose: Post-operative radiotherapy is offered to a majority of breast cancer patients, since it significantly reduces the risk of local recurrence. However, some patients still develop recurrences. Owing to their vital roles in the repair of radiation-induced double-strand breaks, the Mre11/Rad50/Nbs1 (MRN) complex and the ATM protein might be implicated in tumour cell resistance to radiotherapy. The aim of this study was to investigate the expression and predictive role of these DNA repair proteins for the outcome of radiotherapy in breast cancer patients.Patients and Methods: The protein expression of ATM and the proteins in the MRN complex were investigated using immunohistochemistry in tumours from 224 women with early breast cancer, who were randomised to receive post-operative radiotherapy or adjuvant chemotherapy (CMF).Results: Compared to normal breast tissue, the staining intensity of Mre11, Rad50, Nbs1 and ATM was reduced in a majority of the tumours. Weak expression of the MRN complex was correlated to high histological grade and ER negativity (p=0.01 and p=0.0001). Radiotherapy significantly reduced the risk of local recurrence as compared to chemotherapy (p=0.04). The greatest benefit of radiotherapy was seen in patients with moderate/strong expression of the MRN complex (RR=0.27, 95% C.I. 0.098-0.72, p=0.009), whereas patients with negative/weak MRN had no benefit of radiotherapy compared to CMF. These results suggest that an intact MRN complex is important for the tumour cell eradicating effect of radiotherapy.

Nyckelord

Radiotherapy

breast cancer

mre11

rad50

nbs1

MEDICINE

MEDICIN

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)