Breast cancer. Coloured mammogram (X-ray) of a side view of a woman's breast showing a cancerous tumour (blue, upper centre). Breast cancer is the most common cancer in women, affecting one in every 20. The cancer can invade surrounding tissues and spread to other parts of the body (metastasis). Regular self-examination of the breasts, and regular screening using mammography, can help to diagnose the cancer early. The most common treatment after early detection is the surgical removal of the tumour, combined with radiotherapy and chemotherapy. If the cancer has spread, the prognosis is poor.