aetiology

Last edited 09/2019 and last reviewed 10/2020

The cause of gynaecomastia is likely to be an imbalance between oestrogen activity (increased) and androgen activity (decreased) in the breast tissue (1).

Summary of causes (2):

Benign gynaecomastia can be secondary to multiple medical and recreational drugs, as well as many chronic medical conditions.

Physiological

  • neonatal: due to placental oestrogen transfer
  • pubertal: pubertal oestrogen production begins prior to testosterone production due to early maturation of aromatase (catalyzes conversion of androgens to oestrogens). Regression occurs in 90% of cases
  • senile: Age 70+. Up to 65% of men. Due to the reduction in testosterone relative to oestrogen

Drug induced - 10-20% of gynaecomastia is due to prescribed drugs

  • for example
    • Oestrogen containing drugs eg. Bicalutamide, Buserelin, Goserelin
    • Androgen receptor blocking drugs e.g. Cyproterone acetate, spironolactone, flutamide
    • Androgen production inhibiting e.g. Finasteride, ketoconazole, dutasteride

Drug induced - recreational drugs such as marijuana, amphetamines, heroin, methadone

Pathological

  • Adrenal or testicular tumours <3% of gynaecomastia
    • a. Oestrogen or androgen producing tumours
    • b. Aromatase producing tumours
    • c. hCG producing tumours
  • Endocrine
    • a. Primary hypogonadism [10% of gynaecomastia]
    • b. Secondary hypogonadism
    • c. Prolactinoma
    • d. Thyrotoxicosis
    • e. Acromegaly
    • f. Androgen insensitivity
  • Systemic illness
    • a. Liver cirrhosis
    • b. Renal failure
    • c. Malnutrition
    • d. Obesity
    • e. HIV

More detailed information relating to aetiological factors is presented in linked items below.

The aetilogy of gynaecomastia can be classified as:

  • physiological
  • pathological
  • drug-induced
  • idiopathic - especially in the elderly

Reference:

Related pages:

physiological

pathological

drug-induced gynaecomastia