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Other names: Breast mice, breast mouse[1]
Histopathologic image of breast fibroadenoma. Core needle biopsy. H&E stain.
SymptomsRound, firm, and easy to move breast lump up to 3 cm[2][3]
Usual onset15 and 35 years[3]
TypesPericanalicular, intracanalicular[4]
Risk factorsPregnancy, hormone replacement therapy[2]
Diagnostic methodExamination, ultrasound, mammography, needle biopsy[3][1]
Differential diagnosisBreast cancer, phyllodes tumors, lipoma, breast cyst, fat necrosis[3][1]
TreatmentNone, observation, removal by surgery or biopsy[3][1]
Frequency25% of women[3]

Fibroadenomas, also known as breast mice, are a type of non-serious breast tumour.[2] They often feel round, firm, and are easy to move within the breast.[2] They are typically up to 3 cm in size and are not painful.[2][3] In about 70% of cases they occur singularly.[1] They are not associated with breast cancer;[2] though may result in anxiety or unequal breast size.[1]

The cause is unknown.[1] They may become more noticeable during pregnancy or hormone replacement therapy and shrink following menopause.[2] They contain a mixture of connective and glandular tissue.[2] Diagnosis may be supported by examination, ultrasound, mammography, and needle biopsy.[3][1] It involves ruling out other types of breast lumps including breast cancer and phyllodes tumors.[3]

If there are no symptoms, no treatment beyond reassurance and follow-up is required.[3][1] In cases that are bothersome, removal by surgery or biopsy is an option.[3] Other techniques that are being looked at include cryoablation and high-intensity focused ultrasound (HIFU).[3] Fibroadenomas affect about 25% of women.[3] They most often begin between the age of 15 and 35 years.[3] The name breast mice refers to their high mobility within the breast.[1]

Signs and symptoms

Fibroadenomas are non-serious tumours of the breast, most often being seen in women in their 20s and 30s.[5] They are usually solid breast lumps that are:

  • Painless[5]
  • Firm or rubbery[5]
  • Mobile[5]
  • Solitary-round with distinct, smooth borders[5]

People who have a simple fibroadenoma do have an increased risk of developing breast cancer compared to the general population.[5] Complex fibroadenomas may increase the risk of breast cancer slightly.[5]

In the male breast, fibroepithelial tumors are very rare, and are mostly phyllodes tumors. Exceptionally rare case reports exist of fibroadenomas in the male breast; however, these cases may be associated with antiandrogen treatment.[6]


The cause of fibroadenoma is unknown.[1] A connection between fibroadenomas and reproductive hormones has been suggested which may explain why they present themselves during reproductive years, increase in size during pregnancy, and regress post-menopause.[7]

Higher intake of fruits and vegetables, higher number of live births, lower use of oral contraceptives and moderate exercise are associated with lower frequency of fibroadenomas.[8]


A fibroadenoma is usually diagnosed through clinical examination, ultrasound or mammography, and often a biopsy sample of the lump.[9] Suspicious findings on imaging may result in a person needing a biopsy in order to gain a definitive diagnosis. There are three types of biopsies: fine-needle aspiration, core-needle biopsy and surgical biopsy. The method of biopsy depends on the appearance, size and location of the breast mass.[10]


Macroscopic view of fibroadenoma of the breast
Closeup of a fibroadenoma of the breast


The diagnostic findings on needle biopsy consist of abundant stromal cells, which appear as bare bipolar nuclei, throughout the aspirate; sheets of fairly uniform-size epithelial cells that are typically arranged in either an antler-like pattern or a honeycomb pattern. These epithelial sheets tend to show typical metachromatic blue on Diff-Quik staining. Foam cells and apocrine cells may also be seen, although these are less diagnostic features.[9][11] The gallery images below demonstrate these features.

Cellular fibroadenoma, also known as juvenile fibroadenoma, is a variant type of fibroadenoma with increased stromal cellularity.[12][13]


Approximately 90% of fibroadenomas are less than 3 cm in diameter. However, these tumors have the potential to grow reaching a remarkable size, particularly in young individuals. The tumor is round or ovoid, elastic, and nodular, and has a smooth surface. The cut surface usually appears homogenous and firm, and is grey-white or tan in colour. The pericanalicular type (hard) has a whorly appearance with a complete capsule, while the intracanalicular type (soft) has an incomplete capsule.[11]


Fibroadenoma of the breast is a benign tumor composed of a biplastic proliferation of both stromal and epithelial components.[14][15] This biplasia can be arranged in two growth patterns: pericanalicular (stromal proliferation around epithelial structures) and intracanalicular (stromal proliferation compressing the epithelial structures into slit-like spaces).

These tumors characteristically display hypovascular stroma compared to malignant neoplasms.[16][17][11] Furthermore, the epithelial proliferation appears in a single terminal ductal unit and describes duct-like spaces surrounded by a fibroblastic stroma. The basement membrane is intact.[18]

Molecular pathology

Up to 66% of fibroadenomas harbor mutations in the exon (exon 2) of the mediator complex subunit 12 (MED12) gene. In particular, these mutations are restricted to the stromal component.[19][20]


Fibroadenomas can be expected to shrink naturally, so most are simply monitored.[21] Monitoring fibroadenomas involves regular check-ups to make sure that the breast mass is not growing and is not potentially cancerous.[21] Check-ups involve physical examinations performed every 3–6 months and optional diagnostic imaging performed every 6–12 months for 1–2 years.[21] Generally, surgery is only recommended if the fibroadenoma gets larger or causes increased symptoms.[22] They are removed with a small margin of normal breast tissue if the preoperative clinical investigations are suggestive of the necessity of this procedure. A small amount of normal tissue must be removed in case the lesion turns out to be a phyllodes tumour on microscopic examination.[11][23]

Because needle biopsy is often a reliable diagnostic investigation, some doctors may decide not to operate to remove the lesion, and instead opt for clinical follow-up to observe the lesion over time using clinical examination and mammography to determine the rate of growth, if any, of the lesion. A growth rate of less than sixteen percent per month in women under fifty years of age, and a growth rate of less than thirteen percent per month in women over fifty years of age have been published as safe growth rates for continued non-operative treatment and clinical observation.[24]

Some fibroadenomas respond to treatment with ormeloxifene.[25]

Fibroadenomas have not been shown to recur following complete excision or transform into phyllodes tumours following partial or incomplete excision.[11]


There are several non-invasive options for the treatment of fibroadenomas, including percutaneous radiofrequency ablation (RFA), cryoablation, and percutaneous microwave ablation.[26] With the use of advanced medical imaging, these procedures do not require invasive surgery and have the potential for enhanced cosmetic results compared with conventional surgery.[26]


The FDA approved cryoablation of a fibroadenoma as a safe, effective, and minimally-invasive alternative to open surgical removal in 2001.[27] During cryoablation, ultrasound imaging is used to guide a probe into the mass of breast tissue. Extremely cold temperatures are then used to destroy the abnormal cells, and over time the cells are reabsorbed into the body.[28] The procedure can be performed as an outpatient surgery using local anesthesia, and leaves substantially less scarring than open surgical procedures and no breast tissue deformation.[citation needed]

The American Society of Breast Surgeons recommends the following criteria to establish a patient as a candidate for cryoablation of a fibroadenoma:[27]

  1. The lesion must be sonographically visible.
  2. The diagnosis of a fibroadenoma must be confirmed histologically.
  3. The lesion should be less than 4 cm in diameter.

High-intensity focused ultrasound

High-intensity focused ultrasound (HIFU) is a technique for the treatment of tumors of the breast and has shown promising results in the form of complete radiological removal of tumors.[29] An ultrasound beam is focused on a target in the breast and leads to tissue death and protein degradation by raising the temperature in that area.[29] Currently, the use of radiation is recommended in some cases, but HIFU in particular is not part of treatment guidelines.[30] Further research into the usefulness of HIFU, specifically in fibroadenoma, is required before more widespread use of the technique in fibroadenoma.[29]


Of all breast tissue samples taken, fibroadenomas comprise about 50%, and this rate rises to 75% for tissue sample in women under the age of 20 years.[31] Fibroadenomas are more frequent among women in higher socioeconomic classes and darker-skinned people.[31] Body mass index and the number of full-term pregnancies were found to have a negative correlation with the risk of fibroadenomas.[31] There are no known genetic factors that influence the rate of fibroadenomas.[31] The rate of occurrence of fibroadenomas in women have been reported in literature to range from 7% to 13%.[31]


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Salati, SA (7 December 2020). "Breast fibroadenomas: a review in the light of current literature". Polski przeglad chirurgiczny. 93 (1): 40–48. doi:10.5604/01.3001.0014.5676. PMID 33729177.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 "Breast Health: Follow-up after an abnormal mammogram - NCI". 30 October 2014. Archived from the original on 5 September 2023. Retrieved 19 October 2023.
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 Stachs, A; Stubert, J; Reimer, T; Hartmann, S (9 August 2019). "Benign Breast Disease in Women". Deutsches Arzteblatt international. 116 (33–34): 565–574. doi:10.3238/arztebl.2019.0565. PMID 31554551.
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  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 "Fibroadenomas of the Breast". Archived from the original on 13 November 2018. Retrieved 13 November 2018.
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