Hormonal therapy exploits the dependence of certain cancers on endogenous hormones for growth and survival, providing effective treatment with a distinct toxicity profile compared to chemotherapy. Breast cancer and prostate cancer are the most common hormone-sensitive malignancies, and endocrine manipulation forms a cornerstone of their management across all disease stages.
What Is Hormonal Cancer Therapy?
Endocrine therapies work by reducing hormone levels or blocking hormone receptors. In breast cancer, strategies target estrogen signaling through receptor blockade or estrogen production inhibition. In prostate cancer, androgen deprivation therapy reduces testosterone levels or blocks androgen receptor signaling.
Drug Classes and Mechanisms
Selective estrogen receptor modulators (SERMs) such as tamoxifen competitively bind estrogen receptors, acting as antagonists in breast tissue while retaining partial agonist activity in bone and uterus. Tamoxifen is the cornerstone of adjuvant therapy for premenopausal hormone receptor-positive breast cancer and reduces recurrence risk by approximately 50 percent.
Aromatase inhibitors (AIs) including letrozole, anastrozole, and exemestane inhibit the conversion of androgens to estrogens by aromatase in peripheral tissues. They are first-line adjuvant therapy in postmenopausal women and are preferred over tamoxifen due to superior efficacy and reduced thromboembolic and uterine cancer risk.
Fulvestrant is a selective estrogen receptor degrader (SERD) that binds, blocks, and degrades the estrogen receptor. It is used in advanced hormone receptor-positive breast cancer after progression on prior endocrine therapy.
Ovarian suppression through gonadotropin-releasing hormone (GnRH) agonists (goserelin, leuprolide) suppresses ovarian estrogen production in premenopausal women, inducing a reversible menopausal state.
GnRH agonists such as leuprolide and goserelin initially stimulate then suppress pituitary LH and FSH release, reducing testicular testosterone production to castrate levels. They form the backbone of androgen deprivation therapy for prostate cancer.
GnRH antagonists including degarelix and relugolix provide rapid testosterone suppression without the initial flare seen with GnRH agonists. They are used in advanced prostate cancer.
Anti-androgens competitively block androgen receptors. Bicalutamide is a first-generation non-steroidal anti-androgen used in combination with GnRH agonists. Enzalutamide and apalutamide are second-generation agents with higher receptor affinity and additional mechanisms including inhibition of nuclear translocation, effective in castration-resistant prostate cancer.
Abiraterone inhibits CYP17, blocking androgen synthesis in the adrenal glands, testes, and within the tumor itself. It is used with prednisone in metastatic castration-resistant and castration-sensitive prostate cancer.
Therapeutic Uses
Hormone receptor-positive breast cancer is treated with adjuvant endocrine therapy for five to ten years. Advanced disease uses sequential endocrine agents before chemotherapy in the absence of visceral crisis. Prostate cancer is treated with androgen deprivation therapy from diagnosis in advanced stages, with second-generation anti-androgens and abiraterone added in castration-resistant disease.
Adverse Effects
Tamoxifen increases venous thromboembolism and endometrial cancer risk. Aromatase inhibitors cause arthralgias, osteoporosis, and fractures. Androgen deprivation therapy causes hot flashes, decreased libido, erectile dysfunction, fatigue, muscle loss, osteoporosis, and increased cardiovascular and metabolic risk. Enzalutamide may cause fatigue, hypertension, and rare seizures. Abiraterone requires co-administration with prednisone to manage mineralocorticoid excess.
Key Clinical Considerations
Bone health monitoring and prophylaxis with calcium, vitamin D, and bisphosphonates or denosumab is essential for patients on aromatase inhibitors or prolonged androgen deprivation therapy. Cardiovascular risk assessment and management is important given the metabolic effects of hormonal therapies. Resistance to endocrine therapy eventually develops through multiple mechanisms including ESR1 mutations and ligand-independent receptor activation.
Conclusion
Hormonal cancer therapy provides effective, well-tolerated treatment for hormone-sensitive breast and prostate cancers across the disease continuum. Understanding resistance mechanisms and the optimal sequencing of agents is essential for maximizing the durable benefit these therapies provide.
