Mammogram of a female breast showing a non- invasive cancerous tumour which appears as the small, round white object in centre of image. The nipple is visible at left. Mammography is a special X-ray technique that is used to visualise soft tissues of the breast as a means of screening for breast cancer. The majority of breast cancers originate in the mammary ducts; the breast lobular glands are another potential site. Most tumours of either type may show early evidence of invasive (malignant) behaviour. However, both ductal & lobular cancers may exist in a non-invasive stage, being confined to a particular duct or lobule.