Hormone therapy is used to treat breast and prostate cancers. Hormones are used because some cancers are "hormonal dependent" or influenced positively or negatively by the presence of certain hormones.

Hormone therapy can prevent cancer growth or slow tumor progression. This type of treatment is administered either orally or by injection and may be a stand-alone treatment or supplemental to other types of treatment. Unlike chemotherapy, which is stopped at some point, hormone therapy is continued indefinitely, unless or until the cancer returns.