Definition/General
Introduction:
Benign phyllodes tumors are biphasic fibroepithelial tumors of the breast, characterized by a cellular stroma and a benign epithelial component arranged in a leaf-like pattern
They are the most common type of phyllodes tumor, accounting for about 60-75% of cases.
Origin:
They arise from the intralobular stroma of the breast.
Classification:
Phyllodes tumors are classified as benign, borderline, or malignant based on histological features
Benign phyllodes tumors have the least aggressive features.
Epidemiology:
They are most common in women in their 40s
They are rare, accounting for less than 1% of all breast tumors.
Clinical Features
Presentation:
Typically presents as a painless, firm, mobile, palpable breast mass
They can grow rapidly.
Symptoms:
A painless, large breast lump is the most common symptom
The rapid growth can cause a sensation of pressure or discomfort.
Risk Factors:
The exact cause is unknown
They are not strongly associated with the common risk factors for breast carcinoma.
Screening:
On mammography, they appear as large, well-circumscribed, lobulated masses
Ultrasound shows a solid mass, sometimes with cystic spaces.
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Gross Description
Appearance:
A large, well-circumscribed, lobulated mass
The cut surface has a characteristic leaf-like (phyllodes) appearance with whorled, fleshy, gray-white tissue and cystic spaces.
Characteristics:
Benign tumors are typically smaller than malignant ones and do not show necrosis or hemorrhage.
Size Location:
Can occur anywhere in the breast
Size is highly variable.
Multifocality:
Multifocality is rare.
Microscopic Description
Histological Features:
Biphasic tumor with a benign epithelial component and a cellular stromal component
The stroma is more cellular than in a fibroadenoma
The key features for diagnosing a benign phyllodes tumor are: mild stromal cellularity, mild to moderate stromal atypia, low mitotic activity (<5 per 10 high power fields), no stromal overgrowth, and pushing borders.
Cellular Characteristics:
The stromal cells are spindle-shaped with minimal atypia
The epithelial component consists of benign ductal structures.
Architectural Patterns:
The characteristic leaf-like architecture is formed by the proliferation of the stroma into the cystic spaces lined by epithelium.
Grading Criteria:
The diagnosis of benign phyllodes tumor is based on the combination of mild stromal hypercellularity, mild atypia, low mitotic rate, no stromal overgrowth, and pushing margins.
Immunohistochemistry
Positive Markers:
The stromal cells are positive for vimentin and CD34
The epithelial component is positive for cytokeratins.
Negative Markers:
The stromal cells are negative for cytokeratins.
Diagnostic Utility:
IHC is not usually necessary for diagnosis but can be used to differentiate from other spindle cell lesions.
Molecular Subtypes:
Molecular subtyping is not relevant for this benign condition.
Molecular/Genetic
Genetic Mutations:
Mutations in MED12 are common in both fibroadenomas and phyllodes tumors.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
Benign phyllodes tumors have a risk of local recurrence (around 10-20%), but they do not metastasize
The risk of recurrence is related to the adequacy of surgical margins.
Therapeutic Targets:
Treatment is wide local excision with clear margins to reduce the risk of local recurrence.
Differential Diagnosis
Similar Entities:
Fibroadenoma (cellular)
Borderline phyllodes tumor.
Distinguishing Features:
Cellular fibroadenomas have less stromal cellularity and lack the leaf-like architecture
Borderline phyllodes tumors have more pronounced stromal cellularity, atypia, and mitotic activity.
Diagnostic Challenges:
The distinction between a cellular fibroadenoma and a benign phyllodes tumor can be difficult, especially on a core needle biopsy
The presence of a leaf-like pattern and increased stromal cellularity favors a phyllodes tumor.
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]
Prognostic Factors
Prognostic factors: [list factors]
Final Diagnosis
Final diagnosis: [complete diagnosis]