What is endocrine therapy?

Endocrine therapy, also known as hormone therapy or hormonal therapy, is a medical practice that manipulates hormone levels in patients. 

Hormones, classified as peptides, steroids, or amino acid-derived signaling molecules, play a crucial role in regulating vital bodily functions such as metabolism, mood, growth, and reproduction. Imbalances in hormone levels can lead to various health issues, including fertility problems and cancers.  

The approaches to addressing these issues through endocrine therapy vary based on the specific health condition, its severity, and patient-related factors like sex and age. Depending on the situation, endocrine therapy may involve adjusting hormone levels, blocking hormone effects, or inhibiting hormone production, including the removal of hormone-producing glands such as the testes, ovaries, or thyroid.¹ 

Hormone therapy types 

Endocrine therapy targets hormone-sensitive cancers, such as estrogen receptor-positive breast and prostate cancers. It involves estrogen deprivation in breast cancer, progesterone suppression in ovarian cancer, and progestin inhibition in uterine cancer, alongside androgen deprivation for prostate cancer. Neoadjuvant endocrine therapy helps shrink hormone-driven tumors before surgery, while adjuvant endocrine therapy reduces the risk of cancer recurrence post-surgery. 

Among common types of non-oncological endocrine treatments are: 

• Insulin therapy for type 1 diabetes; 

• Growth hormone therapy for growth hormone deficiency (GHD); 

• Thyroid hormone replacement in hypothyroidism and antithyroid therapy in hyperthyroidism; 

• Glucocorticoid and mineralocorticoid replacement in Addison’s disease and antiglucocorticoid therapy in Cushing’s syndrome; 

• Hormone replacement therapy for intersex conditions such as Turner syndrome and Klinefelter syndrome, addressing variations in sex characteristics; 

• Gender-affirming hormone therapy for transgender individuals, involving feminizing or masculinizing sex steroids. 

In some cases, hormonal therapy aims to mitigate side effects from natural hormone production decline due to aging, such as hormone replacement therapy (HRT) for women and androgen replacement therapy (ART) for men. These can potentially help prevent health issues related to low hormone levels and may also be applied to younger patients experiencing surgically induced or premature menopause or hypogonadism. 

Additionally, oral contraception, menstrual suppression, and chemical castration for men with hypersexuality or paraphilias are also forms of endocrine therapy. 

Methods of hormone administration in endocrine therapy 

Endocrine treatments requiring hormone administration employ various methods, each with its own advantages and disadvantages. These methods include: 

• Topical creams and gels; 

• Transdermal patches; 

• Intravaginal rings; 

• Nasal sprays; 

• Inhalers; 

• Pills and tablets; 

• Vaginal or rectal suppositories; 

• Injections; 

• Implants. 

The latter method involves implanting small pellets containing hormones, allowing for a slow release of the substance into the body over time. 

Endocrine therapy drugs 

Since endocrine therapy addresses a wide range of health conditions, the list of associated drugs is extensive and varies by country due to regulatory approvals. Some commonly used hormone therapy medications include: 

• Levothyroxine and liothyronine for thyroid disorders; 

• Insulin and glucagon for diabetes management; 

• Clomiphene and human chorionic gonadotropin (hCG) for fertility treatments; 

• Raloxifene and calcitonin for osteoporosis; 

• Tamoxifen, anastrozole, letrozole, and exemestane for breast cancer; 

• Megestrol, and medroxyprogesterone for endometrial cancer; 

• Leuprolide, goserelin, bicalutamide, and enzalutamide for prostate cancer; 

• Estradiol and testosterone for hormone replacement and gender-affirming therapy.² 

Endocrine therapy side effects 

The side effects of endocrine therapy can differ based on the specific medication used, the condition being treated, its severity, and the patient’s individual profile. For example, less severe side effects inflicted by breast cancer treatment may include night sweats, hot flashes, joint or muscle pain, vaginal dryness, and fatigue.³ In contrast, diabetes patients might experience gastrointestinal issues, weight gain, and hypoglycemia. 

However, some patients may develop more serious side effects, including: 

• Severe heart issues leading to heart failure with certain thyroid, diabetes, and prostate cancer therapies; 

• Deep vein thrombosis, pulmonary embolism, severe bone loss, and endometrial cancer linked to breast cancer treatments, particularly with aromatase inhibitors and long-term Tamoxifen use; 

• Severe liver injury from antithyroid medications. 

References: 

1. “Hormone Therapy to Treat Cancer.” National Cancer Institute.
   https://www.cancer.gov/about-cancer/treatment/types/hormone-therapy 
2. “Metabolic & Endocrine.” Medscape.
   https://reference.medscape.com/drugs/metabolic-endocrine 
3. “Hormone Therapy.” American Cancer Society.
   https://www.cancer.org/cancer/managing-cancer/treatment-types/hormone-therapy.html