Radiotherapy is one of the major modalities in breast cancer treatment. However, resistance to radiotherapy may be a significant factor in the development of local recurrence following surgical resection and radiotherapy. In addition, if patients with radioresistant breast cancers can be identified, harmful side effects from exposure to unnecessary ionizing radiation could be prevented. We aimed to develop novel in vitro models of radio-resistance using breast cancer cell lines and to subsequently identify molecular biomarkers that may be associated with the radioresistant phenotype. We used a combined proteomic (two-dimensional gel electrophoresis/mass spectrometry) and transcriptomic (expression microarrays) screening approach.