Hormone Therapy in oncology, also called hormonal therapy, hormone treatment or endocrine therapy, is treatment that slows or stops cancers whose growth depends on particular hormones. Its principal established uses include hormone-responsive breast and prostate cancers. Rather than directly destroying every rapidly dividing cell, endocrine treatment modifies the hormonal environment on which susceptible malignant cells depend. It can reduce hormone production, prevent hormones from interacting with their receptors, degrade receptors or otherwise disrupt endocrine signalling. The National Cancer Institute describes two broad mechanisms: blocking the body's ability to produce particular hormones and interfering with how hormones act in the body.
The biological basis of Hormone Therapy is the presence of functional hormone signalling within susceptible tumour cells. In breast cancer, tumour tissue is assessed for oestrogen receptors and progesterone receptors, and cancers containing these receptors are classified as hormone receptor positive. Such receptor testing is performed on tumour material and helps determine whether endocrine treatment is likely to be useful.
Hormone receptor status is distinct from HER2 status, so a breast cancer can be hormone receptor positive and HER2 positive, hormone receptor positive and HER2 negative, or have other combinations of biological characteristics. Approximately 80% of breast cancers are hormone receptor positive according to current NCI information, although prevalence varies among populations and classification systems.
In breast cancer, important Hormone Therapy approaches include selective oestrogen receptor modulators such as tamoxifen, aromatase inhibitors such as anastrozole, letrozole and exemestane, selective oestrogen receptor degraders such as fulvestrant, and ovarian suppression in appropriate premenopausal patients. Aromatase inhibitors reduce peripheral oestrogen production and are especially important after menopause, while tamoxifen binds to oestrogen receptors and has tissue-specific effects. The choice depends on menopausal status, tumour characteristics, disease stage, prior treatment, recurrence risk, tolerability and other clinical considerations. These therapies may be used alone in selected settings or combined with other systemic treatments.
Hormone Therapy can be used at different stages of cancer management. In early hormone receptor-positive breast cancer, it may be given after surgery as adjuvant treatment to reduce the likelihood of recurrence. In selected circumstances it can be used before surgery as neoadjuvant treatment. It is also important in recurrent or metastatic hormone-responsive disease, where systemic endocrine treatment can suppress tumour growth and disease-related symptoms. In prostate cancer, androgen deprivation and other forms of hormonal manipulation reduce signalling through androgen-dependent pathways. Endocrine treatment can therefore have curative-intent roles in some early cancers and disease-control or symptom-relieving roles in advanced disease, depending on the specific malignancy and clinical setting.
Hormone Therapy differs fundamentally from hormone replacement therapy even though the terminology can appear similar. Hormone replacement is generally intended to restore or supplement physiological hormone levels for an endocrine or reproductive indication, whereas oncological Hormone Therapy is intended to reduce, block or modify hormonal stimulation of malignant cells. It also differs from chemotherapy because its activity depends on a particular biological dependency rather than general susceptibility of rapidly dividing cells. Hormone Therapy is therefore ineffective against cancers lacking the relevant hormonal dependence. For example, breast cancers that are hormone receptor negative generally do not respond to endocrine treatment directed at oestrogen or progesterone signalling.
Because Hormone Therapy changes systemic endocrine physiology, it can produce adverse effects related to hormonal deprivation or receptor modulation. Depending on the treatment, these can include hot flushes, sweating, sexual or reproductive effects, changes in bone health, joint symptoms, fatigue and alterations in cardiovascular or metabolic risk. The clinical significance of adverse effects depends on the agent, duration of treatment, age, menopausal status and pre-existing conditions. Adherence can be particularly important because endocrine treatment may be prescribed for prolonged periods, and persistent side effects can influence whether patients continue therapy. Clinical management therefore involves considering both anticancer benefit and the practical consequences of long-term endocrine manipulation.
Resistance to Hormone Therapy is a major area of cancer research. Some tumours are intrinsically resistant despite expressing a receptor, while others initially respond and later progress through mechanisms such as altered receptor signalling, changes in downstream pathways, mutations affecting the receptor, activation of alternative growth pathways or changes in tumour-cell populations. In breast cancer, endocrine therapy is frequently combined with targeted agents that inhibit complementary pathways, reflecting the interconnected nature of cancer signalling. Molecular evolution during treatment can make a tumour biologically different from the tumour sampled at initial diagnosis, which explains why reassessment may sometimes be considered when recurrent or metastatic disease develops.
Hormone Therapy illustrates the principle that cancer treatment can be directed against a biological dependency rather than simply against a tumour's anatomical location. Its effectiveness has contributed to major improvements in the management of hormone-responsive breast and prostate cancers and has helped establish biomarker-driven treatment selection as a central component of modern oncology. The treatment may be combined with surgery, radiation, chemotherapy or other systemic therapies according to disease stage and tumour biology. Its role is therefore not confined to a single phase of treatment, and the distinction between endocrine treatment, targeted therapy and broader precision oncology can depend partly on how therapeutic classes are defined.
