Formation of Breast Cysts
Breast cysts form as an aberration of normal lobular involution (ANDI) associated with active secretion of apocrine epithelium under hormonal stimulation. 1
Pathophysiologic Mechanism
The development of breast cysts involves a specific physiologic process rather than a disease state:
Cysts arise from abnormal involution of breast lobules, where the normal age-related regression of breast tissue becomes disrupted, leading to fluid accumulation within the lobular structures 1
Hormonal stimulation drives active secretion by apocrine epithelial cells lining these structures, causing fluid to accumulate and form palpable macrocysts 1
The etiology is multifactorial and not completely understood, though fluctuating hormone levels—particularly estrogen—play a central role in cyst formation 2
Hormonal Influences
The hormonal environment is critical to understanding cyst development:
Cysts predominantly occur in premenopausal women due to higher circulating estrogen levels that stimulate the apocrine epithelium 2
Hormonal imbalances increase cyst risk, with conditions like polycystic ovarian syndrome associated with higher rates of fibrocystic changes and cyst formation 2
Postmenopausal cysts are rare unless the woman is receiving hormonal replacement therapy, which reintroduces the hormonal milieu necessary for cyst development 2
The intracystic fluid contains hormones and growth factors including high concentrations of androgens (particularly dehydroepiandrosterone sulfate) and various polypeptide hormones, reflecting the active hormonal environment within cysts 3, 4
Clinical Context
Understanding the formation mechanism helps contextualize their clinical significance:
Macrocysts occur in approximately 7% of adult women, making them one of the most common benign breast findings 1
Cysts are considered specific clinical entities distinct from the outdated concept of "fibrocystic disease," which has been discarded from modern terminology 1
Simple cysts are essentially benign with no associated increased cancer risk, while complicated cysts carry very low malignancy risk (<2%) and complex cysts have significantly higher risk (14-23%) 5, 6