| Absolute increase in free estrogens |
| Direct secretion from: |
| Maternal-placental-fetal unit |
| Testes |
| Adrenal glands |
| Extraglandular aromatization of precursors |
| Displacement from sex hormone-binding globulin |
| Decreased metabolism |
| Exogenous estrogen administration |
| Decreased endogenous free androgens |
| Decreased secretion |
| Increased metabolism |
| Relative increase in free estrogen/free androgen ratio |
| Androgen insensitivity |
| Congenital defects in androgen receptor structure and function |
| Displacement of androgens from breast androgen receptors by certain drugs |
| Other |
| Estrogen-like effect of drugs |
| Possible enhanced sensitivity of breast tissue |
