Definition/General
Introduction:
Phyllodes tumor with micropapillary carcinoma is an extremely rare malignant phyllodes tumor where the stromal component contains micropapillary carcinoma characterized by small clusters of cells in clear spaces resembling lymphovascular invasion.
Origin:
Develops from intralobular breast stroma with differentiation toward micropapillary carcinoma
May arise through specific genetic alterations leading to micropapillary architecture.
Classification:
WHO Classification categorizes this as malignant phyllodes tumor with heterologous elements
Micropapillary component shows characteristic pseudovascular spaces.
Epidemiology:
Exceptionally rare with fewer than 5 cases reported worldwide
Peak age 45-65 years
Female predominance
Associated with high lymph node metastasis rate similar to pure micropapillary carcinoma.
Clinical Features
Presentation:
Large, firm breast mass
Usually presents as irregular, spiculated mass
May show moderate growth rate
Often clinically suspicious for malignancy.
Symptoms:
Progressive breast enlargement
May be painful due to rapid growth
Skin retraction possible with large tumors
Breast asymmetry
Constitutional symptoms rare.
Risk Factors:
Previous phyllodes tumor history
Older age
Family history of breast cancer
No specific environmental risk factors identified.
Screening:
Often detected on mammographic screening
Clinical examination may reveal spiculated mass
Mammography shows irregular mass with spiculation
Core needle biopsy essential.
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Gross Description
Appearance:
Large, irregular mass with firm consistency
Cut surface shows gray-white areas with possible stellate pattern
Spiculated borders may be present.
Characteristics:
Size typically >3 cm (range 2-10 cm)
Firm consistency
Irregular borders
Gray-white coloration
May have central fibrosis.
Size Location:
Can occur in any breast region
Usually involves moderate breast tissue
Unilateral presentation
May have infiltrative appearance.
Multifocality:
Typically unifocal mass
Micropapillary areas may be multifocal within tumor
Growth pattern may be infiltrative.
Microscopic Description
Histological Features:
Biphasic tumor with epithelial and mesenchymal components
Micropapillary carcinoma areas show small clusters of cells in clear spaces lacking endothelial lining, creating pseudovascular pattern.
Cellular Characteristics:
Small clusters of pleomorphic epithelial cells
Moderate to high nuclear grade
Cells appear to float in clear spaces
Loss of cellular cohesion.
Architectural Patterns:
Micropapillary clusters in pseudovascular spaces
Lack of fibrovascular cores
Stromal retraction artifact
May mimic lymphovascular invasion.
Grading Criteria:
Grade 2-3 typically
Moderate to high nuclear grade
Moderate mitotic activity
Micropapillary architecture >50% for pure type.
Immunohistochemistry
Positive Markers:
EMA positive with reverse polarity
Cytokeratins positive
MUC1 positive with apical pattern
E-cadherin reduced
Epithelial component: CK7+.
Negative Markers:
Estrogen receptor variable
Progesterone receptor variable
HER2 variable
CD31 negative (excludes true vessels).
Diagnostic Utility:
EMA reverse polarity characteristic of micropapillary carcinoma
MUC1 apical staining pattern
CD31 negative excludes lymphovascular invasion.
Molecular Subtypes:
Variable molecular subtype
May be luminal or triple-negative
HER2-enriched possible.
Molecular/Genetic
Genetic Mutations:
PIK3CA mutations common
TP53 mutations variable
MYC amplification possible
Loss of E-cadherin function.
Molecular Markers:
Variable gene expression profile
High proliferation markers
Loss of cell adhesion molecules
Angiogenesis factors.
Prognostic Significance:
Poor prognosis due to high lymph node metastasis rate
Micropapillary component predicts aggressive behavior
Early systemic therapy important.
Therapeutic Targets:
Targeted therapy based on receptor status
Anti-HER2 therapy if amplified
CDK4/6 inhibitors if hormone receptor positive
Aggressive chemotherapy.
Differential Diagnosis
Similar Entities:
Primary micropapillary carcinoma of breast
Invasive ductal carcinoma with micropapillary features
Papillary carcinoma
Lymphovascular invasion.
Distinguishing Features:
Phyllodes with micropapillary: Leaf-like areas, EMA reverse polarity
Primary micropapillary: No phyllodes component
True LVI: CD31+ endothelium.
Diagnostic Challenges:
Recognition of micropapillary features
Distinction from lymphovascular invasion
Assessment of percentage micropapillary component
Immunohistochemical interpretation.
Rare Variants:
Micropapillary carcinoma with squamous differentiation
Mixed micropapillary and ductal carcinoma
Micropapillary with neuroendocrine features.
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]