Hormones and Cancer

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Hormones and Cancer
updated: 21 July 2006
Cancer Research UK


Our bodies are full of hormones that tell our cells what to do. At high levels, these naturally-occurring hormones can increase our risk of cancer by encouraging cells to grow or divide more quickly than usual.

This section will discuss the links between hormones and cancer. You can find out about different sources of hormones and whether they affect your risk of cancer. These include:

naturally-occurring hormones in our bodies and how our reproductive and external hormone sources, such as hormone replacement therapy (HRT) and the contraceptive Pill
chemicals in our environment.


What is a hormone?
Hormones are naturally occurring substances that are produced in specific parts of our bodies and act as chemical messengers. They travel through the blood to control the functions of other tissues and organs.

Some of the best known hormones are oestrogen and testosterone. These are known as ‘sex hormones’ and perform a variety of functions all around our bodies.

How do hormones affect our risk of cancer?
Because they have such important roles, the levels of hormones in our bodies is carefully controlled. If these are too high, they can make our cells grow and divide uncontrollably and stop them from dying when damaged. This can lead to cancer.

Oestrogen. Women with the highest levels of oestrogen and related hormones have over twice the average risk of breast cancer and womb cancer. They may also have higher risks of ovarian cancer.

Testosterone. At the moment, it isn’t clear if high levels of testosterone in men increases the risk of prostate cancer. But we do know that prostate cancer cells depend on testosterone in order to grow.

Insulin. Insulin is most famous for controlling our bodies’ sugar levels, but it has many other functions. High levels of insulin have been linked to cancers of the bowel, womb, pancreas and kidneys.

Insulin also affects the levels of another group of similar hormones called insulin-like growth factors or IGFs. High levels of IGF-1 could increase the risk of prostate, breast and bowel cancers. Many scientists are studying the links between insulin, IGFs and cancer but at the moment, they are still unclear.



What affects our hormone levels?
Reproductive factors. A woman’s hormone levels change when she goes through her menstrual cycle or has children. These ‘reproductive factors’ are linked to risks of hormone-related cancers, such as breast and womb cancer. They include:

being pregnant
having children
the age at which a woman has her first child
whether she breastfeeds
the age at which she starts menstruating
the age at which she goes through menopause
We will be adding more information about these reproductive factors and their links to cancer in the near future.



Lifestyle changes. Reproductive factors are very difficult to control. But this doesn’t mean that there is nothing you can do to prevent hormone-related cancers.

Maintaining a healthy bodyweight can help to keep hormone levels under control. This is especially important in women after the menopause, whose ovaries have stopped making hormones. When this happens, fat cells become the main hormone source.

People who are overweight or obese have much higher levels of hormones such as oestrogen, insulin and IGFs. This may explain why they have higher risks of breast, bowel and womb cancers.

There is also some evidence that drinking too much alcohol and not getting enough physical activity could increase a woman’s levels of oestrogen. This may be why these things also increase the risk of breast cancer.



External sources. Your body makes its own hormones but external sources can also raise or lower your hormone levels. These include:

Hormone replacement therapy (HRT)
The contraceptive Pill
Environmental chemicals that mimic hormones
Drugs that lower hormone levels. Oestrogen and testosterone can fuel the growth of breast and prostate cancer cells respectively. So scientists have designed drugs to fight these cancers by lowering the levels of these hormones or blocking their action.

One of these drugs, tamoxifen, has greatly improved survival rates for breast cancer. It works by blocking oestrogen from interacting with a partner protein, just like a piece of gum can stop a key from fitting in a lock.

Cancer Research UK is funding research to see if drugs that lower hormone levels could help to prevent breast cancer from occurring in the first place. These include tamoxifen and another drug called anastrozole that blocks oestrogen production. You can find more information about these drugs in our website CancerHelp UK.


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Our publications
Breast cancer leaflet
Cervical cancer Leaflet


Find out more
In Healthy Living
Hormones in our environment and cancer
Hormone replacement therapy (HRT) and cancer
The Pill and cancer


Elsewhere on our sites
CancerHelp UK - IBIS 2 (II) trial
CancerHelp UK - Breastfeeding and breast cancer
CancerHelpUK - HRT and cancer risk
The contraceptive Pill and cancer risk
Detailed statistics on hormones and cancer


Elsewhere on the web
Breakthrough Breast Cancer - established risk factors
National Cancer Institute - Pregnancy and breast cancer risk


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