Breast cancer is a malignant tumour that originates in the cells of the breast. Breast cancer occurs predominantly in females, although men can also develop the disease. Male breast cancer accounts for approximately 1% of cases.
Breast cancer can occur at any age. It is more common in women aged over 60, although around one-quarter of women are younger than 50.
Breast cancer can start in the ducts or lobules of the breast. When the cancer cells stay in the ducts and lobules of the breast, this is called non-invasive breast cancer. If the cancer cells spread into the surrounding tissue, this is called invasive breast cancer.
Most breast cancers are ductal carcinomas – this means they have originated in the ducts that carry milk to the nipple and are malignant (cancerous). Less common are lobular carcinomas – these form within the cells that line the lobules which produce milk.
Breast cancer stages
Breast cancer is categorised in stages, according to spread (Stage I, II, III, IV) and size (A, B, C). The stage of the cancer will determine how it is treated.
For example, early breast cancer – or early-stage breast cancer – is invasive cancer that includes Stages I, II and early cases of IIIA. The cancer may have spread to nearby lymph nodes but not to other, distant parts of the body.
Locally advanced breast cancer is typically considered a stage III cancer. It refers to breast cancer cells that may have spread to the lymph nodes in the armpit or other areas near the breast such as the skin, muscle or ribs.
Secondary breast cancer, sometimes called advanced breast cancer or metastatic breast cancer, is Stage IV cancer. It occurs when the breast cancer cells break away and travel through the blood or lymphatic vessels to lodge and grow in another location in the body.