Coloured 3D combined computed tomography (CT) and magnetic resonance imaging (MRI) scans showing a tumour (pink) in a breast, extending to the pectoralis muscle (red). Lymph nodes (green) are also visible. Breast cancer is the uncontrolled growth of irregular breast cells. Breast cancer can present as a breast lump or thickening (often painless), a change in the size or shape of the breast, changes in the appearance of the nipple or areola, or an abnormal fluid discharge from the nipple. Treatment options include combinations of surgery, radiotherapy and chemotherapy.