Why does estrogen cause breast cancer

Genes and hormones increase the risk of breast cancer

When a woman has her healthy breasts removed, the fear must be great. The movie star Angelina Jolie caused a sensation with this step in 2013: Previously, doctors had found a mutation in the cancer gene BRCA1 in her, which allegedly increased her cancer risk to a dramatic 87%1. But Angelina Jolie is an exception - in many ways.

It has long been known that breast cancer is more common in some families. The reason for this is the inheritance of genes that significantly increase the risk of breast cancer. These genes are variants that contain minor deviations - even changing a single letter in the genome can have dramatic consequences. There is evidence that at least eight different genes are involved in the development of breast cancer2.

Inherited risk - the role of BRCA

Two genes stand out - BRCA1 and BRCA2. Hereditary changes in these genes can increase the risk of breast cancer up to 60-80%. However, these gene variants are also very rare - they are only found in one in a hundred women. They therefore only explain some of the diseases: only about a quarter of familial and less than a tenth of all breast cancer cases. Angelina Jolie, who wears a variant of BRCA1, is a special case: In 99% of all women, the risk is many times lower.

In addition, the BRCA genes can be mutated in thousands of different places. How dangerous they are or whether they cause breast cancer at all is still unclear for the majority of these mutations. It is therefore usually difficult to assess the personal risk. Against this background, Angelina Jolie's decision to have both breasts amputated cannot be a general role model - many of those affected also have less radical options open to them3.

In addition to BRCA, variants of at least 60 other genes can increase the risk of breast cancer. However, their influence is significantly less: Almost all of these variants are either very rare or only slightly increase the risk of cancer. However, if a woman carries several of these in her genetic make-up, the risk can increase significantly. But the connections are complex and accurate predictions are difficult. In addition, many genetic risk factors are still undiscovered: Overall, researchers can only explain half of all familial breast cancer cases today4.

Estrogen promotes cancer

But the development of breast cancer does not only depend on cancer genes. The female sex hormone estrogen is also involved - although it does not trigger the cancer, it supports its spread. Even in normal breast tissue, the hormone promotes cell growth. If the first cancer precursors develop, this effect can have tragic consequences: the higher the estrogen level, the higher the risk of cancer. For example, Asian women generally have low levels of estrogen - and a reduced risk of breast cancer5. And in women who develop breast cancer after menopause, estrogen levels are increased by 15%6.

Therefore, all factors that affect women's hormonal balance also have an impact on the development of breast cancer. An early onset of the first menstrual period or old age at menopause can therefore be signs of a higher risk. Pregnancies also play a role: late pregnancies or their absence can increase the risk.

The knowledge that estrogen promotes the spread of breast cancer made a new therapy possible as early as the 1970s - with the active ingredient tamoxifen, which blocks this growth signal. Research has continued down this path, developing a new type of targeted drug that opens up new options for treatment. Researchers hope to find even more effective drugs - so that Angelina Jolie's drastic decision will be superfluous in the future.

1 H. Scowcroft, Angelina Jolie, inherited breast cancer and the BRCA1 gene, CancerResearchUK May 2013 (Link)
2Study: These genes increase the risk of breast cancer, Deutsches Ă„rzteblatt, January 2021 (Link)

Breast cancer

  • Deadly despite early detection more ...
  • Genes and hormones increase the risk more ...
  • Early detection is no longer without risk ...
  • Therapy with Tamoxifen and Herceptin more ...

Skin cancer

  • White skin cancer and black melanoma more ...
  • Sun and genes as triggers more ...
  • Melanomas: Therapy with Vemurafenib and Yervoy more ...

Liver cancer

  • One more global problem ...
  • Viruses and cirrhosis as triggers more ...
  • Only curable at an early stage more ...

Kidney cancer

  • Renal cell carcinoma - the most common type of kidney cancer more ...
  • Unhealthy lifestyle increases the risk more ...
  • Operations and immunotherapies more ...

pulp - the blog

May 6, 2021
Chimera of man and monkey - a means to an end
Researchers inject human stem cells into early embryos of monkeys. However, the long-term goal is human organs in pigs.
more...

Short and sweet

  • around 60 cancer genes increase the risk of developing breast cancer
  • the genes BRCA1 and BRCA2 can increase the risk of breast cancer by up to 60-80%
  • most other cancer genes are either very rare or have little impact
  • the effects of most cancer genes are poorly understood
  • the hormone estrogen promotes the spread of breast cancer