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Hormones are substances that occur naturally in the body.
For example, when boys reach adolescence they grow body hair and their voices break. These changes are caused by the hormone testosterone. The hormones oestrogen and progesterone control the changes that occur during a woman's monthly menstrual cycle, for example periods.
Hormone therapy works by changing the level of hormones in the body, or by blocking the hormones so they can't help cancer cells to grow. (Some cancers need hormones to help them grow and multiply.)
This treatment is also called endocrine therapy or hormone manipulation.
