Breast Care A-Z · Condition · BREASTCYST

Breast cyst

also: simple breast cyst, cystic breast lump, breast cysts

A breast cyst is a fluid-filled sac in the breast — one of the most common causes of a new lump, particularly around the menopause — and it is almost always benign. You may have noticed a new lump or been told it is a cyst; this page explains how cysts are confirmed and treated.

Quick answers

Can a breast cyst be cancer?

Simple cysts — fluid-filled spaces with no solid component on ultrasound — are essentially never cancer. Complex cysts with solid components do have a small risk of being something other than a simple cyst, which is why they are biopsied. The diagnostic pathway is designed to identify the rare exceptions safely.

Will my cyst go away on its own?

Sometimes. Smaller cysts often resolve without intervention, particularly after the menopause. Larger or symptomatic cysts can be drained for immediate relief. There is no clinical urgency to drain an asymptomatic cyst.

Why do I keep getting cysts?

Some women's breast tissue is more prone to forming cysts, particularly in the years approaching the menopause. This is not a sign of anything wrong; it is a pattern that some breasts have. Hormonal influences play a role, including hormone replacement therapy in some women.

BREASTORY ENCYCLOPEDIA · PLATE XXXVII ONCOLOGY · BENIGN CONDITIONS breast cyst fibrocystic change · galactocele fluid-filled epithelial cavities arising from terminal duct lobular units FIG 01 cyst anatomy · ultrasound features · aspiration i simple cyst ii complex cyst iii cyst wall (epithelium) iv surrounding stroma v TDLU origin ULTRASOUND FEATURES Simple: · Anechoic (no internal echoes) · Posterior acoustic enhancement · Thin, smooth wall Complex: · Internal echoes / septation · Thick/irregular wall → biopsy · Reduced posterior enhancement ASPIRATION OUTCOMES Clear/straw fluid → discard Green/brown → benign galactocele Blood-stained → send for cytology Cyst fluid cytology has low diagnostic yield unless blood-stained or residual mass FIG 01 — Cyst anatomy · Breast cross-section showing simple and complex cysts arising from TDLU FIG 02 simple vs complex cyst Simple Cyst Complex Cyst Feature Ultrasound Anechoic, smooth wall Echoes, septation present Wall Thin, regular Thick, irregular Post. enhancement Present (increased) Reduced or absent Aspiration fluid Clear/straw coloured May be blood-stained Cytology Not routinely required Recommended Malignant risk <0.1% ~0.5–2% Management Aspirate if symptomatic Core biopsy advised Recurrence 20–30% after aspiration Variable Symptoms Lump, cyclical tenderness Lump, pain Age peak 40–50 years Any age FIG 03 cyst vs malignant mimic Feature Benign Cyst Malignant Lesion Shape Oval or round Irregular, spiculated Margins Well-defined Ill-defined Internal echoes Absent (simple) Present Posterior Enhancement Shadowing Mobility Mobile Fixed Skin Normal Dimpling/tethering Lymph nodes Normal Enlarged Growth Static / slow Progressive Doppler Avascular Increased vascularity FIG 04 assessment pipeline Assessment Pipeline 1 Lump detected Patient or clinician n 2 Clinical assessment History, examination, 3 Ultrasound First-line imaging — c 4 Aspiration ± Therapeutic + diagnost 5 Cytology if needed Blood-stained fluid or 6 Discharge / follow-up Discharge if resolved; FIG 05 cyst variant tiles Simple Cyst Anechoic, smooth wall, posterior enhancement Complex Cyst Echoes or septation, thick wall, biopsy needed Galactocele Milk-filled cyst, post- lactation, benign Oil Cyst Fat necrosis origin, eggshell calcification Haematoma Blood-filled, post- trauma, resolves slowly Abscess Infected cyst, hot, tender, antibiotic/drain FIG 06 key statistics 1 in 3 women develop breast cysts [1] 40–50 yrs peak incidence by decade [2] >95% of cysts are benign [3] 20–30% simple cyst recurrence rate [4] FIG 07 references References 1. Dixon JM et al. Breast cysts. BMJ 1999;319:1486. 2. Breast Unit Standards NHS England 2023. 3. NICE CG14. Referral for suspected cancer 2023. 4. Houssami N et al. Ultrasound characteristics of breast cysts. Breast 2004. 5. ACR Practice parameter ultrasound-guided breast biopsy 2022. Clinically authored by Dr Fiona Tsang-Wright , FRCS (Gen Surg) GMC 4549831 · ORCID 0000-0003-4801-026X
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Definition
A breast cyst is a benign (non-cancerous) fluid-filled sac that forms in the breast tissue, most common in women in their 40s and early 50s, and is one of the most frequent causes of a new breast lump.

Common questions The questions patients ask first

Can a breast cyst be cancer?
Simple cysts — fluid-filled spaces with no solid component on ultrasound — are essentially never cancer. Complex cysts with solid components do have a small risk of being something other than a simple cyst, which is why they are biopsied. The diagnostic pathway is designed to identify the rare exceptions safely.
Will my cyst go away on its own?
Sometimes. Smaller cysts often resolve without intervention, particularly after the menopause. Larger or symptomatic cysts can be drained for immediate relief. There is no clinical urgency to drain an asymptomatic cyst.
Why do I keep getting cysts?
Some women's breast tissue is more prone to forming cysts, particularly in the years approaching the menopause. This is not a sign of anything wrong; it is a pattern that some breasts have. Hormonal influences play a role, including hormone replacement therapy in some women.
Will my cyst come back after it is drained?
A meaningful minority of simple cysts will recur in the same place after aspiration4. This is not a problem in itself — recurrent cysts are managed with another aspiration if they are uncomfortable, and they often stop recurring after a few cycles. A small minority of repeatedly recurrent cysts are considered for surgical excision3.

A breast cyst is a benign (non-cancerous) fluid-filled sac that forms in the breast tissue, most common in women in their 40s and early 50s, and is one of the most frequent causes of a new breast lump.

Breast cysts are very common. They can appear suddenly, sometimes with discomfort, and can be alarming when first noticed. Diagnosis is usually straightforward on ultrasound, and many cysts need no treatment beyond reassurance — though uncomfortable cysts can be drained in clinic with a fine needle, with immediate relief.

Orientation Why you might be reading about this

You have probably noticed a new lump in your breast and have either been told it is a cyst, or are reading about possible causes. Cysts are one of the most common reasons for a new breast lump, particularly in women approaching the menopause, and they are also one of the simplest things to confirm and treat. This page explains what a breast cyst is, how it is diagnosed, and what (if anything) is usually done about it.

Related terms: Breast lump · Fibroadenoma · Breast ultrasound · Core biopsy · Triple assessment

Definition What a breast cyst is

A cyst is a fluid-filled space that develops within the normal duct system of the breast. The fluid inside is usually clear, straw-coloured, brown, or green; less often it is blood-stained. Cysts can be a few millimetres across, in which case they are usually invisible to examination and noticed only on imaging, or they can grow to several centimetres and present as an obvious lump.

Cysts are most common in women in their 40s and early 50s, becoming less common after the menopause unless a woman is on hormone replacement therapy. They are uncommon in women under 30. The reason for this age pattern is hormonal — cysts are part of the normal cyclical changes that breast tissue undergoes during the reproductive years.

Diagnosis How a breast cyst is diagnosed

Diagnosis is usually quick and straightforward:

  • Clinical examination — a typical cyst feels smooth, mobile, and well-defined, sometimes tender. The texture alone is not diagnostic3.
  • Breast ultrasound — a cyst appears as a well-defined, dark (anechoic), thin-walled space with characteristic acoustic features. A simple cyst on ultrasound is essentially diagnostic1.
  • Mammogram — cysts appear as smooth, round densities; ultrasound is the test that distinguishes a cyst from a solid lump3.
  • Core biopsy is not needed for a typical simple cyst. It is reserved for complex cysts with internal features that warrant tissue sampling12.

In many cases the diagnosis is made and the cyst is drained in the same visit at a one-stop clinic.

Cyst categories Simple, complicated, and complex cysts

Radiologists categorise cysts on ultrasound:

  • Simple cyst — completely fluid-filled, no internal features, classic ultrasound appearance. Essentially never cancer12.
  • Complicated cyst — contains some particulate matter (cellular debris in the fluid), but otherwise has a thin, smooth wall. Almost always benign (malignancy rate <2%)2; usually managed with drainage and follow-up if symptomatic.
  • Complex cyst — has solid components, thickened walls, internal divisions, or other features. Sampled with core biopsy of the solid component (BI-RADS 4); cyst-fluid cytology is not routinely used unless the aspirate is bloody and the cyst fails to resolve1. A small percentage turn out to be something other than a simple cyst2.

This categorisation is on the imaging report; the consultation translates it into a plan.

Treatment Treatment

Most simple cysts need no treatment. They can be left alone if they are not causing symptoms and the diagnosis is clear.

If a cyst is uncomfortable or the patient prefers to have it drained, a cyst aspiration can be done in the same one-stop visit — a quick, minimally uncomfortable procedure using a fine needle under ultrasound guidance, with immediate relief3.

Cysts can recur in the same place after aspiration in a meaningful minority of cases4. Recurrent cysts are not a sign of anything worrying and are usually managed with another aspiration.

At consultation What to discuss with your surgeon

If you have a confirmed simple cyst, the conversation usually covers:

  • Whether to drain it now (for symptoms or preference) or leave it alone (asymptomatic).
  • What to expect if it recurs.
  • Whether new lumps in the future need imaging again, or whether your “cyst pattern” is now established.

For complex cysts, the conversation extends to the biopsy result, the follow-up imaging schedule, and whether surgical excision is being considered.

Resources Further reading

Sources & guidance

Every figure on this page is anchored to a published source. Tap a number in the text or below to jump to the reference.

  1. reference text American College of Radiology (ACR). Breast Imaging Reporting and Data System (BI-RADS) Atlas, 5th edition — Ultrasound. Reston, VA: ACR. 2013 ;Cystic lesions: simple, complicated, complex https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Reporting-and-Data-Systems/BI-RADS Cited for: Ultrasound classification of breast cysts: simple (BI-RADS 2), complicated (largely benign), complex cystic-and-solid (warrants tissue sampling).
  2. cohort Berg WA, Sechtin AG, Marques H, Zhang Z. Cystic breast masses and the ACRIN 6666 experience. Radiologic Clinics of North America. 2010 ;48(5):931–987 doi:10.1016/j.rcl.2010.06.007 Cited for: Malignancy rates by cyst category — essentially zero in simple cysts; <2% in complicated cysts; meaningful risk in complex cystic-solid lesions, hence biopsy of solid components.
  3. guidance Royal College of Surgeons / Association of Breast Surgery. Best Practice Diagnostic Guidelines for Patients Presenting with Breast Symptoms. London: ABS. 2010 ;Section: cystic disease https://associationofbreastsurgery.org.uk/professionals/information-hub/guidelines/2010/best-practice-diagnostic-guidelines-for-patients-presenting-with-breast-cancer-symptoms Cited for: UK pathway: clinical examination + ultrasound for cystic lesions; aspiration in same visit where symptomatic; biopsy reserved for complex cysts.
  4. cohort Vargas HI, Vargas MP, Eldrageely K, Gonzalez KD, Khalkhali I. Outcomes of sonography-based management of breast cysts. American Journal of Surgery. 2004 ;188(4):443–447 doi:10.1016/j.amjsurg.2004.07.006 Cited for: Recurrence after fine-needle aspiration of simple cysts; safety of conservative management of asymptomatic simple cysts.