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The RAD51 135G/C polymorphism is related to the effect of adjuvant therapy in early breast cancer
Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences.
Department of Oncology, karolinska Unvíversity Hospital, Stockholm, Sweden.
Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Pathology and Clinical Genetics.
2015 (English)In: Journal of Cancer Research and Clinical Oncology, ISSN 0171-5216, E-ISSN 1432-1335, Vol. 141, no 5, 797-804 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer Publishing Company, 2015. Vol. 141, no 5, 797-804 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-17954DOI: 10.1007/s00432-014-1859-0ISI: 000352859700003OAI: oai:DiVA.org:liu-17954DiVA: diva2:213082
Available from: 2009-04-27 Created: 2009-04-27 Last updated: 2017-12-13Bibliographically approved
In thesis
1. DNA repair pathways and the effect of radiotherapy in breast cancer
Open this publication in new window or tab >>DNA repair pathways and the effect of radiotherapy in breast cancer
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A large proportion of breast cancer patients are treated with radiotherapy. Ionising radiation induces different DNA damages, of which double-strand breaks are the most severe. They are mainly repaired by homologous recombination or non-homologous end-joining. Different protein complexes have central roles in these repair processes. In addition to the ability to repair DNA damage, cellular radiosensitivity is also affected by mitogenic signals that stimulate survival and inhibit apoptosis. The phosphatidylinositol 3-kinase (PI3-K)/AKT pathway controls cell proliferation, invasiveness and cell survival. AKT is regulated by upstream growth factor receptors, one of them being HER2 (also called ErbB2). HER2 is overexpressed in 15-30% of all breast cancers and associated with poor prognosis.

In this thesis, we have studied factors that affect tumour cell resistance to ionising radiation. In Paper I, the role of HER2/PI3-K/AKT signalling in radiation resistance was investigated in two breast cancer cell lines. The results support the hypothesis that the HER2/PI3-K/AKT pathway is involved in resistance to radiation-induced apoptosis in breast cancer cells in which this signalling pathway is overstimulated.

We also investigated if the protein expression of several DNA repair-associated proteins influence the prognosis and treatment response in early breast cancer. Moderate/strong expression of the MRE11/RAD50/NBS1 (MRN) complex predicted good response to radiotherapy, whereas patients with negative/weak MRN had no benefit from radiotherapy as compared to chemotherapy (Paper II). These results suggest that an intact MRNcomplex is important for the tumour-eradicating effect of radiotherapy. In Paper III, low expression of the BRCA1/BRCA2/RAD51 complex was associated with an aggressive phenotype, an increased risk of local recurrence and good response to radiotherapy.

In Paper IV, we studied if a single nucleotide polymorphism, RAD51 135G/C, was related to RAD51 protein expression, prognosis and therapy resistance. We found that genotype was not correlated to neither protein expression nor prognosis. Patients who were G/G homozygotes had a significant benefit from radiotherapy. The results also suggested that the RAD51 135G/C polymorphism predicts the effect of chemotherapy in early breast cancer.

In conclusion, DNA repair proteins are potential prognostic and predictive markers. The results indicate that proteins in different repair pathways may contribute differently to the effect of radiotherapy. Also, the HER2/PI3-K/AKT signalling pathway protects cells from radiation-induced apoptosis. In the future, it might be possible to target some of these proteins with inhibitory drugs to sensitise tumours to radiotherapy.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 84 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1112
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-17955 (URN)978-91-7393-668-2 (ISBN)
Public defence
2009-05-20, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2009-05-07 Created: 2009-04-27 Last updated: 2009-08-21Bibliographically approved

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Söderlund Leifler, KarinAskmalm Stenmark, Marie

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