How Breast Cysts Develop
Hormonal Mechanisms
Breast cysts develop primarily due to hormonal imbalances characterized by estrogen predominance and progesterone deficiency, leading to hyperproliferation of connective tissue (fibrosis) followed by epithelial proliferation and eventual cyst formation. 1
The pathophysiology involves several key hormonal factors:
- Estrogen activity and progesterone deficiency are the fundamental drivers, with nearly all patients with gross breast cysts demonstrating low progesterone levels 2, 1
- Contrary to older assumptions, absolute hyperestrogenism is actually rare—only 8.7% of women with gross breast cysts have truly elevated estrogen levels, while 65.3% are actually hypoestrogenic 2
- The critical factor is the relative imbalance between estrogen and progesterone rather than absolute hormone elevations 3, 1
Prolactin's Role
Prolactin involvement is more nuanced than previously thought:
- Normal baseline prolactin levels are found in 96.7% of women with breast cysts 2
- However, women with recurrent cysts show significantly increased prolactin secretion when stimulated with metoclopramide, suggesting abnormal prolactin dynamics rather than baseline hyperprolactinemia 2
- The role of prolactin in human breast disease remains incompletely understood despite its clear importance in animal models 4
Dynamic Hormonal Changes
Recent evidence emphasizes that dynamic hormonal fluctuations and chronobiological rhythms (daily, menstrual, and seasonal) are more important than static hormone levels in cyst pathogenesis 3. This explains why:
- Cysts predominantly occur in premenopausal women with cycling hormones 5, 1
- The disease progresses with advancing premenopausal age and peaks in women during their 40s 1
- Fibrocystic changes typically regress during the postmenopausal period when hormonal fluctuations cease 1
Postmenopausal Considerations
Breast cysts in postmenopausal women are extremely rare unless the patient is on hormonal replacement therapy, which reintroduces the hormonal fluctuations that drive cyst formation 5. In postmenopausal women not on hormone therapy, simple cysts are seen with a frequency of 17-24%, with 53% disappearing completely over time and 28% remaining stable 6.
Clinical Implications
The hormonal basis explains why:
- Low-estrogen oral contraceptives with progestin components effectively treat fibrocystic disease by opposing estrogen action 1
- Cyclic progestogen administration (progesterone or medroxyprogesterone acetate) successfully modulates the mammary effects of estrogen 1
- Conditions causing hormonal imbalances, such as polycystic ovarian syndrome, increase the risk of fibrocystic changes 5