Definition/General
Introduction:
A fibroadenoma is the most common benign tumor of the female breast
It is a biphasic tumor composed of a proliferation of both epithelial and stromal elements.
Origin:
It arises from the terminal duct-lobular unit (TDLU).
Classification:
Fibroadenomas are classified as benign fibroepithelial tumors
Variants include juvenile fibroadenoma and complex fibroadenoma.
Epidemiology:
They are most common in young women, with a peak incidence in the 20s and 30s
They can be multiple and bilateral in up to 20% of cases.
Clinical Features
Presentation:
Presents as a painless, firm, mobile, well-circumscribed, rubbery mass
They are often described as a "breast mouse" due to their mobility.
Symptoms:
A painless, mobile lump is the most common symptom
They can increase in size during pregnancy and lactation.
Risk Factors:
They are hormonally responsive and can grow in response to estrogen.
Screening:
On mammography, they appear as a well-circumscribed, oval mass that may have "popcorn-like" calcifications
On ultrasound, they are a well-defined, hypoechoic mass.
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Gross Description
Appearance:
A well-circumscribed, encapsulated, firm, gray-white mass that bulges from the cut surface.
Characteristics:
The cut surface is whorled and may have slit-like spaces.
Size Location:
Size is variable, but they are typically 1-3 cm
They can occur anywhere in the breast.
Multifocality:
Can be multiple and bilateral.
Microscopic Description
Histological Features:
A biphasic tumor with a proliferation of benign glands and stroma
The glands are lined by a double layer of epithelial and myoepithelial cells
The stroma is typically bland and fibroblastic.
Cellular Characteristics:
The epithelial and stromal cells are benign, with no atypia or mitotic activity.
Architectural Patterns:
Two main patterns are described: intracanalicular (stroma compresses the glands into slit-like spaces) and pericanalicular (stroma surrounds open, rounded glands)
Most fibroadenomas have a mixed pattern.
Grading Criteria:
This is a benign lesion.
Immunohistochemistry
Positive Markers:
The epithelial cells are positive for cytokeratins and ER
The myoepithelial cells are positive for p63 and calponin
The stromal cells are positive for vimentin and CD34.
Negative Markers:
Not typically required for diagnosis.
Diagnostic Utility:
IHC is not usually necessary for diagnosis but can be used to confirm the presence of a myoepithelial layer.
Molecular Subtypes:
Molecular subtyping is not relevant for this benign condition.
Molecular/Genetic
Genetic Mutations:
Recurrent mutations in the MED12 gene are found in a high percentage of fibroadenomas.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
Fibroadenomas are benign
Simple fibroadenomas are not associated with an increased risk of breast cancer
Complex fibroadenomas (which have features like cysts >3mm, sclerosing adenosis, epithelial calcifications, or papillary apocrine change) are associated with a small increased risk.
Therapeutic Targets:
Treatment is usually conservative (observation)
Excision may be performed for large or symptomatic lesions, or if there is diagnostic uncertainty.
Differential Diagnosis
Similar Entities:
Phyllodes tumor
Tubular adenoma.
Distinguishing Features:
Phyllodes tumors have a more cellular stroma, often with a leaf-like architecture, and can show stromal atypia and mitoses
Tubular adenomas are composed almost exclusively of small, closely packed tubules.
Diagnostic Challenges:
The main challenge is distinguishing a fibroadenoma from a benign phyllodes tumor on a core needle biopsy, as the stromal cellularity can be variable.
Rare Variants:
Juvenile fibroadenoma is a rapidly growing variant seen in adolescents
Giant fibroadenoma is a term for fibroadenomas >5 cm or >500g.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type], measuring [size] cm in greatest dimension
Diagnosis
[diagnosis name]
Classification
Classification: [classification system] [grade/type]
Histological Features
Shows [architectural pattern] with [nuclear features] and [mitotic activity]
Size and Extent
Size: [X] cm, extent: [local/regional/metastatic]
Margins
Margins are [involved/uninvolved] with closest margin [X] mm
Lymphovascular Invasion
Lymphovascular invasion: [present/absent]
Lymph Node Status
Lymph nodes: [X] positive out of [X] examined
Special Studies
IHC: [marker]: [result]
Molecular: [test]: [result]
[other study]: [result]
Final Diagnosis
Final diagnosis: [complete diagnosis]