Breast cysts are circumscribed fluid collections that most commonly occur in premenopausal women. The typical presentation includes single or multiple breast masses of variable size that may be tender. Because cysts cannot be reliably distinguished from a solid mass on palpation or mammography, the diagnostic evaluation requires a breast ultrasound. Based on ultrasound findings, breast cysts are characterized as simple, complicated, or complex. Complex breast cysts are associated with an increased risk of malignancy and should be biopsied. Complicated breast cysts are typically benign; a biopsy should be considered if there is clinical suspicion of malignancy. Simple breast cysts are benign and seldom require any further diagnostics. Management depends on the type of cyst and risk of malignancy and includes surveillance, therapeutic aspiration, and surgical excision.
- Simple breast cysts are a common cause of breast lesions identified on examination or imaging. 
- Peak incidence (of simple cysts): 35–50 years of age; most common in premenopausal women 
Epidemiological data refers to the US, unless otherwise specified.
- Maybe asymptomatic (detected incidentally) 
- Single or multiple breast masses
- May be tender
- Variable size (microcysts, gross cysts, clusters) and texture (smooth, soft, firm)
- Usually mobile
Cystic and solid breast masses cannot reliably be distinguished on physical examination alone. 
- Follow age-appropriate breast imaging for a palpable breast mass.
- Use targeted ultrasound to evaluate any masses identified on mammography. 
- Tailor further management based on imaging findings.
- Simple breast cyst: no further diagnostic evaluation 
- Complex breast cyst: ultrasound-guided core needle biopsy or excisional biopsy to rule out concomitant malignancy
- Complex breast cyst: surveillance, therapeutic aspiration, or biopsy depending on clinical concern for malignancy
Ultrasound is the preferred modality for differentiating between cystic and solid breast masses. 
Biopsy is recommended for all breast cysts with suspicious features (e.g., doppler flow, thick septations or walls, solid components). 
Cytological evaluation is recommended if bloody fluid is obtained on therapeutic or diagnostic aspiration. 
Characterization of breast cysts 
Breast cysts are best characterized on ultrasound. On mammography, a breast cyst appears as a round, circumscribed mass (i.e., indistinguishable from a solid breast mass). 
|Types of breast cysts |
|Simple breast cyst||Complicated breast cyst||Complex breast cyst|
|Characteristic features on ultrasound|| || || |
|Risk of malignancy|| || || |
Mammography cannot reliably distinguish between a solid and cystic breast mass. A breast mass detected on mammography should be additionally evaluated on ultrasound. 
Management of simple breast cysts 
- Asymptomatic cysts: : no intervention required; most resolve spontaneously 
Symptomatic cysts : Consider ultrasound-guided fine needle aspiration. 
- Simple cysts generally collapse on aspiration.
- Aspirate is typically serous and can be discarded.
Simple breast cysts are not associated with an increased risk of breast cancer. Routine breast cancer screening is appropriate. 
Management of complicated breast cysts 
Management depends on patient preferences and clinical concern for malignancy and includes the following.
- Surveillance: close clinical and imaging follow-up over 1–2 years 
- Therapeutic fine needle aspiration: Any bloody aspirate should be sent for cytology.
Core needle biopsy is indicated if there is clinical suspicion for malignancy, such as:
- Lesion persists after aspiration
- Bloody aspirate obtained
- Increasing cyst size (on surveillance) 
Routine breast cancer screening is appropriate for patients with complicated breast cysts that have been proven benign on biopsy or have not increased in size over a period of surveillance. 
Management of complex breast cysts 
Perform an ultrasound-guided core needle biopsy or excisional biopsy in all patients. 
Benign lesion on biopsy 
- Follow-up at 6 and/or 12 months for 1 year.
- No growth on surveillance: Routine breast cancer screening is appropriate.
- Indeterminate lesion or radio-pathological discordance: surgical excision