The RAD51 135G/C polymorphism is related to the effect of adjuvant therapy in early breast cancer

• Purpose: A single-nucleotide polymorphism, RAD51 135G/C, in the untranslated region of the RAD51 gene has been found to elevate breast cancer risk among BRCA2 carriers. The purpose of this study was to investigate if this polymorphism is related to RAD51 protein expression, prognosis of early breast cancer and if it contributes to resistance to radiotherapy or cyclophosphamide/5-fluorouracil/methotrexate (CMF) chemotherapy.Methods: We genotyped 306 patients with early breast cancer, who were randomised to receive post-operative radiotherapy or CMF chemotherapy, for the RAD51 135G/C polymorphism. Expression of RAD51 protein was evaluated with immunohistochemistry.Results: The frequency of C-allele was 15.4% (including three C/C homozygotes). There was no correlation between genotype and protein expression pattern in tumours. Patients who were homozygous for the wildtype G/G genotype had a significant benefit of radiotherapy (RR=0.32, 95% C.I. 0.16-0.64, p=0.001). CMF chemotherapy significantly reduced the risk of distant recurrence during the first 20 years in patients who had the C-allele (RR=0.29, 95% C.I. 0.10-0.88, p=0.03), whereas patients who were G/G homozygotes had no benefit from chemotherapy over radiotherapy (RR=1.09, 95% C.I. 0.77-1.6, p=0.61). There was a significant interaction between chemotherapy and genotype (p=0.02). Genotype was not related to the rate of distant recurrence among patients treated with radiotherapy.Conclusion: Breast cancer patients who were homozygous for the wildtype G allele had a significant benefit of radiotherapy. The results suggest that the RAD51 135G/C polymorphism predicts the effect of CMF chemotherapy in early breast cancer.

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