Definition/General

Introduction:
-A simple fibroadenoma is a fibroadenoma that does not contain any of the complex features (cysts >3mm, sclerosing adenosis, epithelial calcifications, or papillary apocrine change)
-It is the most common type of fibroadenoma.
Origin: It arises from the terminal duct-lobular unit (TDLU).
Classification: It is a subtype of fibroadenoma.
Epidemiology:
-They are most common in young women, with a peak incidence in the 20s and 30s.

Clinical Features

Presentation: Presents as a painless, firm, mobile, well-circumscribed, rubbery mass.
Symptoms: A painless, mobile lump is the most common symptom.
Risk Factors: Hormonally responsive.
Screening:
-On mammography, they appear as a well-circumscribed, oval mass
-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.
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
-There are no complex features.
Cellular Characteristics:
-The epithelial and stromal cells are benign, with no atypia or mitotic activity.
Architectural Patterns:
-Can be intracanalicular, pericanalicular, or mixed.
Grading Criteria: This is a benign lesion.

Immunohistochemistry

Positive Markers: The IHC profile is similar to that of a conventional fibroadenoma.
Negative Markers: Not applicable.
Diagnostic Utility: IHC is not usually necessary for diagnosis.
Molecular Subtypes: Not applicable.

Molecular/Genetic

Genetic Mutations: Recurrent mutations in the MED12 gene are common.
Molecular Markers: No specific molecular markers are routinely used for diagnosis.
Prognostic Significance: Simple fibroadenomas are not associated with an increased risk of breast cancer.
Therapeutic Targets:
-Treatment is usually conservative (observation)
-Excision may be performed for large or symptomatic lesions.

Differential Diagnosis

Similar Entities:
-Complex fibroadenoma
-Phyllodes tumor.
Distinguishing Features:
-Complex fibroadenomas have complex features
-Phyllodes tumors have a more cellular stroma and a leaf-like architecture.
Diagnostic Challenges: The main challenge is distinguishing a simple fibroadenoma from a benign phyllodes tumor on a core needle biopsy.
Rare Variants: Not applicable.

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]