Complex Breast Cysts

A ‘complex‘ or ‘complicated‘ breast cyst, refers to cysts that contain something besides clear fluid. Usually something harmless like old blood clot or debris in a cyst.

Brittany Brittany
OK, I’m relaxing. Don’t tell me to relax.


They are on the upper end of the continuum of abnormalities that can sometimes happen to breast cysts. Simple breast cysts are fluid filled, and with a uniformly thin and smooth wall to their oval shape. A complex breast cyst, however, contains a good percentage of solid elements suspended within the fluid, and may also feature segmentation (septation) and some regions of the cyst wall that are ‘thicker‘ than others.

Dr. Halls Dr. Halls
Simple cysts are supposed to have thin walls and contain only clear fluid.


Complex breast cysts account for approximately 5% of breast cysts that are screened, and are usually followed up more closely in terms of time interval, and are sometimes biopsied. There is a very very small chance that a complex breast cyst could be associated with malignant breast cancer, so they merit a higher degree of scrutiny.

Here’s an ultrasound picture of a complicated breast cyst.
complex breast cyst ultrasound

Dr. Halls Dr. Halls
One look at this, and I know it’s not cancer.


Ultrasound features of complicated breast cysts

There are no standard definitions or signature features of a complex breast cyst. They are a heterogeneous group of lesions with different presentations. On ultrasound a complex breast cyst will typically be evaluated in terms of internal echoes, presence or absence of posterior enhancement (evidence of an intracystic mass), thin septations, and a thickened and/or irregular wall (lobulations). But the results of the ultrasound can influence the strategy for followup evaluation or treatment.

The radiologist will be looking for…

Findings of septations (thin walls dividing the cysts into segments) is really of little concern. What the radiologist is looking for is hard evidence of an intracystic mass, which would be indicative of neoplastic cell growth, and that would probably lead to a histological evaluation. Even so, the chances of the neoplasm being breast cancer is very low.

Dr. Halls Dr. Halls
If a breast cyst contains a septation, it’s not a cancer. Cancers grow into round shapes, not slender dividing-walls between fluid.


The decision to biopsy remains subjective

Findings of internal echoes without a distinctly visible solid mass or, alternatively, an ‘anechoic’ lesion with no posterior-wall enhancement would be a bit of a judgement call. It likely means that various particles are floating in the cystic fluid and, and the cysts is extremely likely to be completely benign. ( It could be floating cholesteral crystals, blood, pus, or milk of calcium crystals.) The decision to biopsy, or aspirate, or simply follow up with observation would be somewhat subjective in this instance.

Higher risk of malignant association when there are irregular lobule shapes in the margin

The presentation of complex cysts and actual malignancy development, when it rarely occurs, can be a little bit irrational. The presence of an intracystic mass (probable neoplasm) does not statistically correlate with higher risk of malignancy. But a thick cystic wall, lobulation (irregular lobule shapes in the wall), and hyperechogenecity (many internal echoes), particularly when occurring in combination, may be associated with higher risk of underlying malignancy.

Here is a picture of a complex cyst on a mammogram. To the radiologist, it could be anything, solid or a liquid cyst, so it would need an ultrasound.
complex breast cyst

Rate or risk of malignancy associated with complex breast cysts

The vast majority of complex breast cysts turn out to be benign. As for those that eventually show as developing due to malignant breast cancer, there is quite a range of opinion as to the ‘malignancy rate’. This is probably due to the fact that there is no consistent definition of a complex cyst. Some studies place the rate as high as 63%, others as low as 0.3 %. So, the best answer is, ‘what does the histological evaluation say”. The ultrasound confirmation of a complex breast cyst cannot be generalized as any having any particular or consistent rate of association with breast cancer. Of interest, personal or family history of breast cancer, and menopausal status appear to have no bearing on the development of a malignant neoplasm.

Biochemically distinct types of breast cysts?

One of the trends in cancer research is to look for different biochemical profiles, or ‘markers’ which tend to be associated with particular types of breast cancers or benign lesions.

This page’s information on biochemical markers is getting old. This page on immunohistochemistry is up to date.

Different cells may release different proteins and other chemicals, and that can give clues as to various cell growths and patterns that may be developing. With breast cysts, there does appear to be a tendency towards two basic ‘lining patterns’ : those lined with apocrine epithelium, and those lined with flat epithelium. (Apocrine epithelial cells are basically secretion cells, while ‘flat epithelium’ refers to a flat or columnar ‘stacking pattern’ or layering of normal epithelial cells.) The different cyst-lining cell patterns can also be measured biochemically using [Na+]/[K+], ( the ‘sodium to potassium ratio’ ) of the cystic fluid. There is some suggestion that cysts with ‘low electrolyte’ readings ( higher potassium and less sodium) may indicate a higher risk for breast cancer involvement, but this is purely speculative at this time.

If the ‘wall’ of a complex cystic breast mass is getting thicker, there may be additional issues.

By way of translation, this ‘biochemical-analysis’ approach for evaulating breast cysts suggests that where the epithelial wall is ‘getting thicker’ by adding certain types of cells, the risk of malignant association may be higher.

The lobulated cyst

The word lobulated, refers to the surface of something that is fairly rounded. A peach is an example of a surface that isn’t perfectly spherical. A peach has a cleft causing an indentation in the surface. That cleft in the surface makes the peach a little “lobulated” on that part of it’s surface. Cysts can be like that peach, and might show an outward bulge, or an inward indentation on part of its surface.

I don’t use personally use the word lobulated for cysts, Because, it causes people to search for the meaning of it, and get anxiety for no good reason.

A lobulated cyst, referring only to the surface of it, is just a cyst. On the other hand, a lobulated solid nodule has different significance altogether. A solid nodule that bulges in a way that isn’t a perfect sphere, can indicate that some internal parts of the nodule are growing faster than other parts, which is a mild clue the solid nodule might be cancer. But since a cyst has nothing growing inside it, the lobulated cyst surface is caused from outside the cyst. Probably, the cyst is simply lying against a fibrous band or blood vessel that doesn’t stretch as easily as everything else around the cyst. So I hope you relax about the lobulated cyst.


Shall we Q and A together?

  • What is a complex breast cyst? A sister having two extra-marital affairs and holding it all together. No, that’s just wishful thinking.
  • What is complicated about a breast cyst? Nobody knows how cysts can get blood or grunge in them, or fibrin balls that look like internal nodules. It’s complicated, like affairs.
  • Should it be removed? What is the treatment of a complicated breast cyst? Don’t remove it. Only if it is big enough to hurt, then a radiologist can aspirate it with a needle.
  • What symptoms and why? It can hurt, because it has expanded into tissue where it the surrounding tissue says, who invited you, quit crowding me, you’re so pushy. And nerve endings for pain sensation start sending signals of pain to your brain.
  • What percent of complex cysts are cancerous? What are the chances of being cancer? Exactly not Zero, but very close.
  • Where do cysts grow and form? Anywhere in the fibro-glandular cone of breast tissue, but not in the pure fat. Short-answer, almost anywhere.
  • What color is breast cyst fluid? Normally clear yellow, or resembling tea color or beer color. It might have a slight tinge of red color in it. A complicated cyst would have some extra colors, looking a little green, cloudy, or more red color in the fluid. If you looked at the fluid in a glass vial, you might see speckled debris floating.
  • When to aspirate or remove the cyst? If the radiologist recommends it, go ahead and do it. Or, if the cyst hurts you, YOU can ask for it to be drained or removed. Aspiration is easier.
  • Why do they grow? Can it burst or rupture? They don’t burst or rupture unless someone punches really hard at them. They grow to the size where surrounding pressure stops them, then they stop growing.



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  2. Venta LA, Kim JP, Pelloski CE et al. Management of complex breast cysts. AJR Am J Roentgenol 1999;173:1331-1336.
  3. Tea, MM., Grimm, C., Bikas, D., Kroiss, R., Fink-retter, A., Kubista, E., Wagner, TM., The validity of complex breast cysts after surgery. Journal of Clinical Oncology, 2007 ASCO Annual Meeting Proceedings Part I. Vol 25, No. 18S (June 20 Supplement), 2007: 1519
  4. Tea, MM., Grimm, C., Kroiss, R., Kubista, E., Wagner, T., Sonographic characterization of malignant cystic breast lesions. 2008 Breast Cancer Symposium. American Society of Clinical Oncology.
  5. Foley, CS., Ong, JS., Bevington, E. , The Royal Australasian College of Surgeons Annual Scientific Congress, Perth 9-13 May 2005
  6. Omori LM, Hisa N, Ohkuma K, et al. Breast masses with mixed cystic-solid
    sonographic appearance. J Clin Ultrasound 1993;21:489-495
  7. Lindfors l(K, O’Connor J, Acredolo CR, Liston CE. Short-interval follow-up mammography versus immediate core biopsy of benign breast lesions: assessment of patient stress.AJR 1998;17l:55-58
  8. Mannello, F., Gazzanelli, G., Prostate-specific antigen (PSA/hK3): a further player in the field of breast cancer diagnostics? Breast Cancer Research 2001, 3: 238-243.

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