Breast cancer develops from breast tissue, usually showing itself as a lump in the breast, or a change in breast shape or skin texture. Breast cancer usually develops in the cells that line the milk ducts (ductal carcinomas) and lobules (lobular carcinomas) that supply the ducts with milk. Survival rates vary by tumour type, extent of the disease, and someone’s age, but tend to be high. About 80-90% of patients survive five years after their diagnosis. The Breast Cancer GeCIP Domain will use the 100,000 Genomes Project to better understand how changes (mutations) in someone’s DNA may have caused a tumour to form. They are also interested in how DNA changes might change someone’s risk of developing cancer. The group will also investigate how mutations in the tumour itself can influence how it develops and reacts to treatment. They hope to identify patients where alternative treatments can be repurposed and made more effective.