Breast cancer. Coloured mammogram (X-ray) showing a malignant (cancerous) tumour (pink) of the breast. This is colloid carcinoma, an adenocarcinoma that has arisen from the epithelial lining of mammary lobules. Breast cancer is the most common cancer in women. It can be treated by excision of the tumour if it is caught early. Radiotherapy and chemotherapy are often used as well as surgery to prevent the tumour from regrowing. If the cancer is not diagnosed before it spreads (metastasizes) to other parts of the body the outlook is worse. However, surgery, radiotherapy and chemotherapy can prolong life. Regular screening by mammography of women in middle age can help to diagnose the condition early.