The male breast: gynecomastia and male breast cancer
- Lesion
A swollen male breast is usually gynecomastia from a hormone imbalance; breast cancer in men is rare, often linked to BRCA2 and hormone-receptor positive.
What it is
The male breast has ducts but almost no lobules. Gynecomastia, the commonest male breast lesion, is a benign enlargement caused by too much estrogen effect relative to androgen: it is physiologic in newborns, adolescents and older men, and pathologic with Klinefelter syndrome, cirrhosis, testicular tumours, hyperthyroidism, obesity and many drugs. Male breast cancer is rare, peaks in older men, is strongly associated with BRCA2 mutations and Klinefelter syndrome, and is nearly always ER-positive; it reaches the skin and chest wall early because there is little breast tissue.
Structure
- Gynecomastia early (florid) phase: ductal epithelial hyperplasia with periductal oedema; late phase: fibrous stroma with less epithelial proliferation.
- Male breast cancer: hard subareolar mass that invades skin and pectoral muscle early; histology as in women, lobular types rare.
Step by step
- The balance between estrogen and androgen action on breast tissue shifts toward estrogen.
- Duct epithelium and periductal stroma proliferate, forming a subareolar disc of tissue (gynecomastia).
- Removing the cause (drug, tumour, liver disease) can reverse early gynecomastia; long-standing tissue becomes fibrotic.
- In men with BRCA2 mutation, Klinefelter syndrome or high estrogen exposure, a duct cell can transform into carcinoma.
Clinical notes
- Gynecomastia in a young man with small testes suggests Klinefelter syndrome; with a testicular mass, a hormone-secreting tumour.
- A hard, painless, eccentric mass in an older man is a cancer until proven otherwise.
- Male breast cancer has a similar prognosis to female breast cancer stage for stage, but is often diagnosed later; all affected men are offered BRCA testing.
Test yourself
Think of the answer, then tap the question to see it.
Why does cirrhosis cause gynecomastia?
The diseased liver breaks down estrogen poorly and more androgen is converted to estrogen, so estrogen effects predominate.
Which germline mutation is most associated with male breast cancer?
BRCA2.
What receptor status do most male breast cancers have?
They are estrogen-receptor positive.
Elsewhere in DurgiPedia
- Aromatase (CYP19A1)
- The male gonadal axis and spermatogenesis
- Breast: ducts, lobules and changes with life stage
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Gynecomastia (StatPearls (NCBI Bookshelf), 2026); Male Breast Cancer Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2026); BRCA2 gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.