About breast cancer

The biology of breast cancer

What is breast cancer? 

Breast cancer occurs when abnormal cells in the breast grow in an uncontrolled manner. It occurs in both men and women, but women are at greater risk due to their breast development and lifelong exposure to oestrogens. Cells that grow abnormally can form tumours. Breast cancer occurs when breast tumours spread. There is generally a long period between breast tissue changes and the development of breast cancer.

How does breast cancer start ?

DNA plays a central role in the development of all cancers, including breast cancer. Like other cells in the body, breast cells contain DNA which provides instructions for cell growth and division. When a cell divides its DNA is copied precisely. But occasionally a mistake known as a “mutation” occurs that may be passed on to other cells. Over time mutations accumulate and their combined effects lead to breast cancer. The more often a cell divides the greater the risk of mutations occurring and accumulating.

What “causes” breast cancer ?

There is no simple cause of breast cancer. A variety of risk factors come together to make you more, or less, susceptible. Some of these risk factors are inherited, some are incurred throughout your life and others are present in the environment in which you live.

Naturally occurring oestrogens (and some other hormones in our bodies) can influence the risk of developing breast cancer, mainly because of their ability to increase rates of cell division and promote the growth of oestrogen-responsive tumours.

Modern-day living is increasing our risk of getting breast cancer, with those born in earlier generations or in less well-developed regions having a lower risk of developing the disease.

For more information visit our susceptibility page.

What are the most common types of breast cancer?

Breast cancer is a diverse group of diseases. It may be invasive or non-invasive.    

The most common types of invasive breast cancer include:   

  • Invasive breast cancer of no special type (NST), formally known as invasive ductal carcinoma, where cancer cells have grown through the lining of the milk ducts into surrounding breast tissue. It is called NST as when cells are viewed under a microscope, they have no special features. It accounts for around 70% of all invasive breast cancers.    
  • Invasive lobular breast cancer is where cancer cells in the lobules (milk-producing glands) have spread into surrounding breast tissue. It accounts for around 15% of all invasive breast cancers.   
  • Inflammatory breast cancer is a rare, fast-growing type of breast cancer caused by breast cancer cells blocking the small lymph channels in the breast and skin. In this type of breast cancer, the skin of the breast looks red and inflamed. It accounts for around 1-5% of invasive breast cancers.   
  • Paget’s disease of the breast is a rare type of breast cancer that causes change to the skin of the nipple, similar to eczema. 
  • Hormone receptor-positive cancers are those that have additional receptors for oestrogen, progesterone and/or human epithelial growth factor 2 (HER2+).  Around 75% of breast cancers are oestrogen receptor-positive (ER+). Cells from these tumours produce additional oestrogen receptors (proteins which bind oestrogen) and depend on oestrogen to grow. 
  • Triple-negative breast cancer does not have additional receptors for oestrogen, progesterone or HER2. It is more common in younger women and tends to be more aggressive and more difficult to treat. Around 15% of breast cancers are triple-negative.  
  • Non-invasive breast cancer is an early form of breast cancer, which remains localised to the breast. The most common form is ductal carcinoma in situ (DCIS); if left untreated DCIS may become invasive.  Another common type of non-invasive breast cancer is lobular carcinoma in situ (LCIS). This type of carcinoma is not cancerous (so does not spread), although its presence is correlated with an increased chance of developing cancer at a later stage.   

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If you share our concerns about the links between harmful chemicals and breast cancer, please consider donating to help fund our next important project. By understanding the causes of breast cancer we can reduce the chances of our loved ones being diagnosed in the future. Thank you.