Normal breasts

• Healthy females’ breasts are mainly made up of fatty tissue and contain special milk-producing glands called lobules. These are connected to a network of ducts which carry milk to the nipple for breastfeeding
• Ligaments and muscles in the chest wall help to support breast tissue
• Breasts vary in shape and size
• They change during periods and pregnancy, and also with age

What is cancer?

• The tissues that make up our bodies’ organs (e.g. brain and heart) are composed of billions of tiny cells
• The genetic information (DNA) inside these cells ensures they divide, grow and die in a carefully controlled way
• This allows the body to grow new tissues and repair damaged ones
• When this process goes wrong, cells can multiply and grow out of control and form a tumour

Breast cancer

• Is the name given to cancers that have first developed in breast tissue
• There are many different types

Benign and cancerous tumours

• Some tumours are benign (non-cancerous); tending to grow slowly and be confined to one part of the body
• Tumours that are malignant (cancerous) usually grow more quickly than benign tumours, invading and destroying surrounding tissues and potentially spreading to other organs

Non-invasive breast tumours

• When we talk about breast cancer we normally mean tumours that grow into the surrounding breast tissue, called ‘invasive breast cancer’
• However, sometimes cancerous changes develop within the lobules or ducts but do not break out into the surrounding tissue
• The name given to cancerous changes that form within ducts is Ductal Carcinoma In Situ, or DCIS
• Similarly, cancerous changes that form within lobules are called Lobular Carcinoma In Situ or LCIS  
• It is difficult to estimate how often DCIS or LCIS will develop into invasive breast cancer, but it is believed that if left untreated, DCIS will develop into invasive breast cancer in up to 50 per cent of cases

Spread

• Cells can split off from the original breast cancer site and spread (metastasise) to other parts of the body where they produce new, secondary tumours.