Estrogen and Cancer. National Cancer Institute
 

<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td align="left" nowrap="nowrap" valign="center">Slide 7

</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" height="100%" valign="center" width="1">http://www.cancer.gov/images/red-px.gif</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" valign="center" width="100%">Estrogen and Cancer

</td><td class="pptRightNav" align="right" valign="center"> http://www.cancer.gov/images/UC-leftarrow.gif<img alt="Next Section >" src="http://www.cancer.gov/images/UC-rightarrow.gif" border="0"></td></tr></tbody></table>Paradoxically, estrogen can be both a beneficial and a harmful molecule.
The main beneficial effects of estrogen include its roles in

1. programming the breast and uterus for sexual reproduction,
2. controlling cholesterol production in ways that limit the buildup of plaque in the coronary arteries, and
3. preserving bone strength by helping to maintain the proper balance between bone buildup and breakdown.

Unfortunately, in addition to these important beneficial effects, estrogen can also be harmful. The most serious problem arises from the ability of estrogen to promote the proliferation of cells in the breast and uterus. Although this ability to stimulate cell proliferation is one of estrogen’s normal roles, it can also increase a woman’s chance of developing breast or uterine cancer.
http://www.cancer.gov/PublishedConte...ors/slide8.gif

Re: Estrogen and Cancer. National Cancer Institute
 

<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td align="left" nowrap="nowrap" valign="center">Slide 8

</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" height="100%" valign="center" width="1">http://www.cancer.gov/images/red-px.gif</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" valign="center" width="100%">Estrogen and Breast Cancer

</td><td class="pptRightNav" align="right" valign="center"> http://www.cancer.gov/images/UC-leftarrow.gif<img alt="Next Section >" src="http://www.cancer.gov/images/UC-rightarrow.gif" border="0"></td></tr></tbody></table>During each menstrual cycle, estrogen normally triggers the proliferation of cells that form the inner lining of the milk glands in the breast.
If pregnancy does not occur, estrogen levels fall dramatically at the end of each monthly menstrual cycle. In the absence of high estrogen levels, those milk gland cells that have proliferated in any given month will deteriorate and die, followed by a similar cycle of cell proliferation and cell death the following month. For the average woman, this means hundreds of cycles of breast cell division and cell death repeated over a span of roughly 40 years, from puberty to menopause.
But how do these estrogen-induced cycles of breast cell proliferation increase the risk of developing cancer?
http://www.cancer.gov/PublishedConte...ors/slide9.gif

Re: Estrogen and Cancer. National Cancer Institute
 

<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td align="left" nowrap="nowrap" valign="center">Slide 9

</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" height="100%" valign="center" width="1">http://www.cancer.gov/images/red-px.gif</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" valign="center" width="100%">Cancer Arises from DNA Mutations in Cells

</td><td class="pptRightNav" align="right" valign="center"> http://www.cancer.gov/images/UC-leftarrow.gif<img alt="Next Section >" src="http://www.cancer.gov/images/UC-rightarrow.gif" border="0"></td></tr></tbody></table>Cancer is caused by DNA damage (i.e., mutations) in genes that regulate cell growth and division.
Some mutations are inherited, while others are caused by exposure to radiation or to mutation-inducing chemicals such as those found in cigarette smoke. Mutations also can occur spontaneously as a result of mistakes that are made when a cell duplicates its DNA molecules prior to cell division.
When cells acquire mutations in specific genes that control proliferation, such as proto-oncogenes or tumor suppressor genes, these changes are copied with each new generation of cells. Later, more mutations in these altered cells can lead to uncontrolled proliferation and the onset of cancer. (For more information on how gene mutations cause cancer, see Understanding Cancer.)
http://www.cancer.gov/PublishedConte...rs/slide10.gif

Re: Estrogen and Cancer. National Cancer Institute
 

<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td align="left" nowrap="nowrap" valign="center">Slide 10

</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" height="100%" valign="center" width="1">http://www.cancer.gov/images/red-px.gif</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" valign="center" width="100%">Estrogen-Induced Proliferation of Existing Mutant Cells

</td><td class="pptRightNav" align="right" valign="center"> http://www.cancer.gov/images/UC-leftarrow.gif<img alt="Next Section >" src="http://www.cancer.gov/images/UC-rightarrow.gif" border="0"></td></tr></tbody></table>Although estrogen does not appear to directly cause the DNA mutations that trigger the development of human cancer, estrogen does stimulate cell proliferation.
Therefore, if breast cells already possess a DNA mutation that increases the risk of developing cancer, these cells will proliferate (along with normal breast cells) in response to estrogen stimulation. The result will be an increase in the total number of mutant cells, any of which might thereafter acquire the additional mutations that lead to uncontrolled proliferation and the onset of cancer.
In other words, estrogen-induced cell production leads to an increase in the total number of mutant cells that exist. These cells are at increased risk of becoming cancerous, so the chances that cancer may actually develop are increased.
http://www.cancer.gov/PublishedConte...rs/slide11.gif

Re: Estrogen and Cancer. National Cancer Institute
 

<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td align="left" nowrap="nowrap" valign="center">Slide 11

</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" height="100%" valign="center" width="1">http://www.cancer.gov/images/red-px.gif</td><td>http://www.cancer.gov/images/spacer.gif</td><td align="left" valign="center" width="100%">Estrogen-Induced Proliferation and Spontaneous New Mutations

</td><td class="pptRightNav" align="right" valign="center"> http://www.cancer.gov/images/UC-leftarrow.gif<img alt="Next Section >" src="http://www.cancer.gov/images/UC-rightarrow.gif" border="0"></td></tr></tbody></table>Even in women who do not have any mutant breast cells, estrogen-induced proliferation of normal breast cells may still increase the risk of developing cancer.
The reason involves DNA. A cell must duplicate its DNA molecules prior to each cell division, thereby ensuring that the two new cells resulting from the process of cell division each receive one complete set of DNA molecules. But the process of DNA duplication occasionally makes mistakes, so the resulting DNA copies may contain a small number of errors (i.e., mutations). If one of these spontaneous mutations occurs in a gene that controls cell growth and division, it could lead to the development of cancer.
Proliferation of normal cells from exposure to estrogen creates a vulnerability to spontaneous mutations, some of which might represent a first step on the pathway to cancer.
http://www.cancer.gov/PublishedConte...rs/slide12.gif