Pilar Cyst on the breast

A pilar cyst is a build up of fluid and keratin just under the skin, that can develop around the root-sheath of hair follicles. A pilar cyst is a sub-type of epidermoid cyst, and they are often described using the same general term. They are also sometimes referred to as a ‘wen‘, a ‘Isthmus-catagen cyst‘, or a trichilemmal cyst.

I just want to let you know that this page is kind of getting a little bit out-dated, but it is still very useful. However, I have created a newer version of this page with more up-to-date information on Pilar Breast Cysts.

Pilar cysts tend to form in areas of high hair concentrations, and about 90% of them form on the scalp. The other 10% tend to be formed in various areas of the body, and rarely on the breast. Essentially a pilar or trichilemmal cyst forms when large amounts of keratin are deposited in the ‘root sheath‘ area of a hair follicle, within a short time span.


Breast pilar cysts are benign

Pilar cysts are smooth and movable, and usually a women concerned about a possible breast cancer ‘lump‘ will bring it to the attention of her family physician. Generally speaking, pilar cysts have no symptoms. But, they can become infected, in which case they can become red, swollen, and painful. Pilar cysts are non-cancerous (benign).

There are exceedingly rare reports of pilar cysts which become cancerous, but if a woman brings a lump to the attention of breast cancer screening physicians and finds out it is a pilar cyst, this is good news. It is not breast cancer.

Pilar cysts on the breast often occur in multiples

The development of a pilar cyst is far more common in women than in men, and they tend to occur in older women the most. About 70% of the time they occur in multiples, and are ‘solitary‘ about 30% of the time. Up to 10% of the population will likely develop one or more pilar cysts at some point in their lives.

No one knows exactly what causes a pilar cyst, but it has been suggested that they form due to the ‘budding‘ from the external root sheath (the trichilemmal). Pilar cysts are believed to be ‘genetically pre-determined‘, as they tend to run in families.

Pilar Tumors (on the breast)

Very rarely, pilar cysts may show rapid (proliferative) cell growth and become more solid. These are called ‘pilar tumors‘. They are non-cancerous, but they can grow aggressively and become so large that they have to be surgically removed.

Usually, the clinical presentation of a proliferative pilar tumor (PPT) is of a long-standing pilar or other epidermoid cyst that slowly progresses to a mass, often with a history of inflammation.

Pilar tumors (also called trichilemmomas) are clinically benign, but they can show mitotic cells, nuclear atypia, and dyskeratotic cells (cells which have changed into a ‘white-plaque‘ form), and this can be a misleading (incorrect) indicator of possible skin carcinoma. (However, it would be very unlikely to be mistakenly identified as breast cancer).

Pilar breast tumors grow quickly and can metastasize

On mammogram, a pilar tumor may appear as a lobulated, well-circumscribed mass, and externally the skin may be ulcerated and atrophied. Pilar tumors, occuring on the breast or anywhere else, have to be followed a little more closely.

While they are mostly benign, they have been known to grow in a highly proliferative way locally, and even to metastasize (the ability to metastasize more or less defines ‘malignancy) So, the concern would be that while a proliferative pilar tumor is not really causing any problems, it might start to develop on a critical organ or the brain, where it could cause serious problems.

Trichilemmomas usually range in size from 1 to 10 cm in diameter, but, they can really grow sometimes, even reaching sizes up to 25 cm in diameter.


Treatment of pilar cysts on the breast

Since pilar cysts are benign, not cancerous, and almost always have no association with breast carcinoma at all, it is really not necessary to treat them. But, they can grow and at a certain point cause a cosmetic concern, so they are sometimes drained, or surgically removed.

Of course, if the cyst has become infected, those symptoms will most likely be treated with oral antibiotics.

For further reading, I suggest you visit this page which has some information on epidermoid cysts of the breast, as well as this page for sebaceous breast carcinoma.


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  8. Alzaraa, A., Ghafoor, I., Yates, A., Dhebri, A.:Sebaceous carcinoma of the skin of the breast: a case report. J Med Case Reports. 2008; 2: 276.
  9. Ye, J. Nappie, O., Swanson, PE, Patterson, JW., Wick MR., Proliferating pilar tumors: A clinicopathologi study of 76 cases with a proposal for definition of benign and malignant variants. Am J Clin Pathol 2004; 122:566-74.
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  11. Sabate, JM., Clotet, M., Gomez, A., De las Hras, P., Torrubia, S., Salinas, T.:Radiologic Evaluation of Uncommon Inflammatory and Reactive Breast Disorders. March 2005 RadioGraphics, 25, 411-424.
  12. Pandya, K., Radke, F., Benign Skin Lesions: Lipomas, Epidermal Inclusion Cysts, Muscle and Nerve Biopsies. Surgical Clinics of North America – (June 2009) Volume 89, Issue 3
  13. Man, B. Salm, R. Azzopardi, JG., Pilar tumor: A distinctive type of trichilemmoma. Dagn Histopathol 1982;5:157-67

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