Breast cancer. Light micrograph of a section through breast tissue showing adenocarcinoma (purple lobes) within a mammary duct. This invasive, cancerous tumour arises from the duct's epithelial lining. Breast cancer has a peak incidence in the decade before the menopause. Surgical treatment may involve lumpectomy (removal of the tumour) or mastectomy (removal of the breast) and is often combined with use of radiotherapy and/or chemotherapy. Magnification unknown.