Breast cancer still represents a serious health problem and is currently the most frequent malignancy in the female population in developed countries. In Cyprus, there are 300 new cases annually. In the present study, histology, electron microscopy, immunohistochemistry, and Western blot analysis were used to investigate 100 cases of invasive breast carcinoma. In addition, mutation analysis for the BRCA1 gene was carried out in patient DNA from 26 families with multiple cases of breast/ovarian cancers. Of note are the results of molecular biology which show that there are no germline truncating mutations in the BRCA1 gene in these 26 Cypriot breast cancer families. Furthermore, Western blot analysis revealed the presence of multiple BRCA1 bands in homogenates of tumor and normal tissues, and immunoelectron microscopy showed the presence of nuclear staining for BRCA1 antibodies.