Breast cancer protein. Molecular model of breast cancer type 1 susceptibility (BRCA1) protein. This protein is found in breast and other tissue, where it helps to repair DNA (deoxyribonucleic acid) strands that have double-stand breaks. If the DNA cannot be repaired it tags the cell for destruction. Certain mutations in the BRAC1 protein can prevent it from repairing damaged DNA, leading to the affected cells multiplying uncontrollably and forming a tumour. Mutations in BRAC1 increase the risk of breast, ovarian, fallopian tube and prostate cancers.