What is breast cancer?

The breast is made up of thousands of individual cells that are constantly being renewed and replaced. Cancer occurs when this process of cell renewal and division goes wrong and cells start multiplying out of hand.

The breast is composed of about 10 to 15 different sections, known as lobes, which are divided into smaller parts called lobules. It is here that breast milk is produced. Lobules are connected to the nipple via a network of tubes known as ducts.

Breast cancer is not one disease, but many. More than three-quarters of all breast cancers occur in the ducts, and about 10 per cent in the lobes. When the cancer hasn't spread beyond the ducts or lobes it is known as 'in situ', meaning 'in one place'. This is good news because it means your cancer has been caught at an early stage.

As a result of the widespread introduction of mammography five to ten fold more breast cancers are now being picked up at this stage.

Invasive carcinoma is cancer that has spread to local tissues, surrounding tissues, lymph nodes or other organs. Cancer cells use the lymph system (which transports tissue fluid back to the blood) to get into the blood stream and from here travel throughout the body.

The remaining breast cancers are rare types, such as Paget's disease and inflammatory carcinomas. Paget's disease (named after the doctor who first described it) is a kind of breast skin cancer that appears as an itchy rash around the nipple and its surrounding pigmented area (known as the areola). Inflammatory carcinoma occurs when the skin over the breast becomes inflamed and swollen because the skin lymph vessels are blocked by cancer.