Oestrogen stimulates the growth and division of breast cells as part of normal development. Increased oestrogen concentrations are linked to the development of some breast cancers.After the menopause, the ovaries stop producing oestrogen, but fat cells in the breast continue to produce it. Women who are exposed to more oestrogen over their lifetime, for example because of higher body fat, early puberty or a late menopause, have a higher risk of breast cancer.How increased oestrogen may lead to a tumour:
• Oestrogen binds to the oestrogen receptor, which acts as a transcription factor. It can switch on genes that promote cell division, such as proto-oncogenes. If such a gene is mutated, or is over-expressed because of high oestrogen, cells divide uncontrollably.
• Once a tumour has formed, its cells can make oestrogen themselves. This raises the local oestrogen concentration, which stimulates more division: an example of positive feedback.
• More cell division means more DNA replication, so there is more chance of mutations, including in tumour suppressor genes.Tumours whose cells have oestrogen receptors are called oestrogen receptor positive. They can be treated with drugs such as tamoxifen, which binds to the oestrogen receptor and stops oestrogen binding, so the receptor does not activate transcription. Other drugs reduce the amount of oestrogen made.When interpreting data on oestrogen and breast cancer, remember that a correlation does not prove that oestrogen causes the cancer. Other factors, such as age and genotype, must be taken into account.
• Oestrogen binds to the oestrogen receptor, which acts as a transcription factor. It can switch on genes that promote cell division, such as proto-oncogenes. If such a gene is mutated, or is over-expressed because of high oestrogen, cells divide uncontrollably.
• Once a tumour has formed, its cells can make oestrogen themselves. This raises the local oestrogen concentration, which stimulates more division: an example of positive feedback.
• More cell division means more DNA replication, so there is more chance of mutations, including in tumour suppressor genes.Tumours whose cells have oestrogen receptors are called oestrogen receptor positive. They can be treated with drugs such as tamoxifen, which binds to the oestrogen receptor and stops oestrogen binding, so the receptor does not activate transcription. Other drugs reduce the amount of oestrogen made.When interpreting data on oestrogen and breast cancer, remember that a correlation does not prove that oestrogen causes the cancer. Other factors, such as age and genotype, must be taken into account.