Do hormone changes cause breast cysts?

Hormonal Changes and Breast Cysts

Yes, hormonal changes do cause breast cysts, as evidenced by the presence of benign breast entities including cysts in individuals exposed to hormone therapy. 1

Mechanism of Cyst Formation

• Breast cysts develop as an aberration of normal lobular involution associated with active secretion of apocrine epithelium under hormonal stimulation 2
• The same breast pathology that occurs in cisgender women, including cysts, can be found in transgender women treated with gender-affirming hormone therapy 1
• Mammary development includes the formation of ducts, lobules, and acini in response to hormonal stimulation, creating the structures where cysts can form 1

Hormonal Influences on Breast Cysts

• Fluctuating hormone levels are believed to be associated with fibrocystic changes characterized by adenosis, fibrosis, and cyst formation 3
• Estrogen exposure plays a significant role in breast tissue development and cyst formation, with higher levels of estrogen in premenopausal women contributing to the prevalence of fibrocystic changes 3
• Postmenopausal women on hormone replacement therapy can develop fibrocystic changes including cysts, while these changes are extremely rare in postmenopausal women not on hormone therapy 3, 4

Types of Breast Cysts and Hormonal Profiles

• Breast cysts can be categorized based on their potassium/sodium (K+/Na+) ratio into three types, with different hormonal profiles in each type 5:
  • Type I cysts (K+/Na+ ratio ≥ 1): Higher estradiol, dehydroisoandrosterone, and prolactin levels
  • Type II cysts (K+/Na+ ratio < 1 but ≥ 0.1): Higher progesterone and testosterone contents
  • Type III cysts (K+/Na+ ratio < 0.1): Lower hormone levels overall

Hormone-Related Risk Factors for Breast Cysts

• Clinical macrocysts occur in approximately 7% of adult women 2
• Conditions causing hormonal imbalances, such as polycystic ovarian syndrome, have been associated with an increased risk of fibrocystic changes 3
• In a study of women with gross breast cysts, approximately half of those over 55 years of age were taking hormonal supplements 4

Hormonal Abnormalities in Women with Breast Cysts

• Women with gross breast cysts typically show normal prolactin levels (96.7% of cases) but may have increased prolactin secretion when stimulated by metoclopramide, especially in cases of recurrent cysts 6
• Low progesterone activity is common in women with gross breast cysts 6
• Contrary to expectations, high estrogen levels appear infrequently in women with gross breast cysts, with most patients showing low estrogen activity 6

Clinical Implications and Management

• Breast cysts can be safely aspirated in most cases as the primary management approach 2
• Multiple recurrent cysts may justify short-term therapy with medications like danazol 2
• There is evidence that multiple recurrent cysts are associated with a small but significant increase in breast cancer risk 2
• Type I breast cyst fluid is considered a marker for "active" gross cystic disease of the breast and may be associated with increased breast cancer risk 5

Special Considerations

• Transgender women can experience benign breast entities, including cysts, as part of gender-affirming hormone therapy 1
• Transgender women can also experience nipple discharge related to hormone-induced hyperprolactinemia 1
• Complex cysts presenting in rare demographics (such as postmenopausal women not on hormone therapy) warrant further evaluation to exclude malignancy 3