Breast cancer. Coloured magnetic resonance imaging (MRI) scan of a carcinoma (pink) in a side view of the breast of a 38-year-old woman. The area at upper right (orange) is pectoral muscle. The woman has a P53 gene abnormality that predisposes her to carcinomas: cancers of epithelium, the tissue that lines the skin and internal body organs. The same gene makes her sensitive to ionizing radiation and explains the use of an MRI scan instead of a more common mammogram that uses X-rays. Breast cancer is the most common cancer in women. Regular self- examination and diagnostic scans can lead to early diagnosis and treatment by surgical removal.