Tamoxifen Therapy in Men

Primary FDA-Approved Use: Male Breast Cancer

The American Society of Clinical Oncology recommends tamoxifen 20 mg daily for 5 years as the standard adjuvant therapy for hormone receptor-positive male breast cancer following surgery 1, 2, 3
Male breast cancer is predominantly hormone receptor-positive (99% estrogen receptor-positive), making tamoxifen highly effective 2, 3
Men who complete 5 years of tamoxifen and remain at high risk of recurrence may be offered an additional 5 years of therapy 1, 2

Tamoxifen acts as a selective estrogen receptor modulator (SERM) that competitively blocks estrogen receptors in breast tissue, preventing estrogen's growth-promoting effects on cancer cells 4
The drug demonstrates a 62% relative risk reduction for ER-positive tumors but has no efficacy against ER-negative tumors 4

Tamoxifen 20 mg daily increases gonadotropins (LH, FSH) and testosterone levels in men with idiopathic oligozoospermia and central hypogonadism 5

Men treated with tamoxifen have an increased incidence of thrombotic events, with over 80% occurring in the first 18 months of treatment 6, 7, 5
Testosterone/androgen supplementation should NOT be used by men with breast cancer, as testosterone converts to estrogen via aromatase, potentially stimulating hormone receptor-positive cancer 6, 7, 8, 3

Do not use aromatase inhibitors alone in men for breast cancer treatment, as they are less effective; if tamoxifen is contraindicated, combine an aromatase inhibitor with a GnRH agonist/antagonist 1, 2, 3
Monitor closely for thrombotic events, especially during the first 18 months of therapy 6, 7, 5

For breast cancer: Initial 5-year duration is standard, with consideration for extended therapy in high-risk patients 1, 2
The risk of breast cancer recurrence continues through 15 years after primary treatment and beyond, requiring long-term surveillance 6, 8