About breast cancer

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 woman, 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 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 and this may be passed on to other cells. Over time mutations accumulate and their combined effects may 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 factors come together to make you more, or less, susceptible. Some of these factors are inherited, some are incurred throughout your life and others are present in the environment in which you live. Collectively these factors are described as “risk factors”.

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 about how susceptible you may be see our Susceptibility page.

What are the most common types of breast cancer?

Breast cancer is a diverse group of diseases. Sub-types have different properties in relation to hormone sensitivity and invasiveness as well as menopausal status.

  • Invasive ductal breast cancer occurs in epithelial cells that line the breast ducts and accounts for around 80% of all breast cancers. Invasive lobular breast cancer occurs in lobes and accounts for around 10% of breast cancers.
  • Hormone receptor positive cancers are those that grow in response to high concentrations of oestrogen, progesterone and/or human epithelial growth factor 2 (HER2). The most common of these is oestrogen receptor positive cancer. Cells from these tumours produce additional oestrogen receptors and depend on oestrogen to grow.
  • Triple negative breast cancer is a rarer type of breast cancer which does not have additional receptors for oestrogen, progesterone or HER2. It is more common in younger women and tends to be more aggressive.
  • In situ breast carcinoma (also called 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 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. By donating now you can feel proud of helping our scientists to conduct their crucial work. Thank you.  

A £10 donation today will help fund our research into the causes of breast cancer so we can prevent breast cancer for future generations.


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