Definition/General
Introduction:
Phyllodes tumor is a rare fibroepithelial neoplasm of the breast characterized by leaflike architecture with epithelial and stromal components
On FNAC, diagnosis is challenging due to overlap with fibroadenoma, requiring careful assessment of stromal cellularity and atypia
Accounts for <1% of all breast tumors but represents 2-3% of fibroepithelial lesions.
Origin:
Arises from intralobular stroma and can develop de novo or from pre-existing fibroadenoma
Transformation rate from fibroadenoma to phyllodes tumor is 0.1-0.3%
Both components (epithelial and stromal) are derived from breast tissue.
Classification:
WHO classification recognizes three categories based on stromal features: benign (mild atypia, <5 mitoses/10 HPF, circumscribed), borderline (moderate atypia, 5-9 mitoses/10 HPF), and malignant (marked atypia, ≥10 mitoses/10 HPF, infiltrative borders).
Epidemiology:
Mean age 35-45 years, decade younger than fibroadenoma
Peak incidence in 4th decade
Rare in adolescents and elderly
No significant racial predilection
Bilateral occurrence extremely rare (<1%).
Clinical Features
Presentation:
Rapidly enlarging, well-circumscribed breast mass
May reach large size (giant phyllodes >10 cm)
Mobile mass with smooth surface
Skin changes rare unless very large.
Symptoms:
Painless breast lump with rapid growth over weeks to months
Large tumors may cause breast asymmetry
Ulceration possible in giant tumors
Nipple discharge uncommon.
Risk Factors:
Previous fibroadenoma
Hormonal factors unclear
Genetic syndromes rare (Li-Fraumeni)
No clear association with breast cancer family history.
Screening:
Clinical breast examination for rapidly growing masses
Mammography shows oval to lobulated mass
Ultrasound demonstrates heterogeneous echogenicity with cystic areas
MRI shows heterogeneous enhancement.
Master Phyllodes Tumor Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Well-circumscribed mass with bosselated surface
Cut surface shows leaflike projections into cystic spaces
Gray-white to tan coloration
Fleshy consistency with variable firmness.
Characteristics:
Leaflike (phyllodes) architecture on cut surface
Cystic spaces of varying sizes
Smooth pushing borders
Hemorrhage and necrosis in malignant cases
Calcification uncommon.
Size Location:
Size ranges 2-30 cm (mean 5-6 cm)
Any breast quadrant may be involved
Larger than typical fibroadenoma
Giant phyllodes may involve entire breast.
Multifocality:
Usually solitary lesions
Multifocal disease rare
Bilateral occurrence exceptional
Local recurrence possible if incompletely excised (5-15% benign, 20-30% malignant).
Microscopic Description
Histological Features:
Biphasic tumor with epithelial and stromal components
Leaflike papillary projections lined by benign epithelium
Stromal hypercellularity distinguishes from fibroadenoma
Malignant cases show sarcomatous transformation.
Cellular Characteristics:
Epithelial component: benign ductal epithelium with myoepithelial layer
Stromal component: variable cellularity and atypia
Benign: uniform spindle cells
Malignant: pleomorphic stromal cells with high mitotic rate.
Architectural Patterns:
Intracanalicular growth pattern predominates
Leaflike projections into epithelium-lined spaces
Stromal condensation around ducts
Loss of leaflike pattern in malignant areas with overgrowth.
Grading Criteria:
Based on stromal mitotic count, nuclear atypia, and borders
Benign: <5 mitoses/10 HPF
Borderline: 5-9 mitoses/10 HPF
Malignant: ≥10 mitoses/10 HPF
Stromal overgrowth >40% in malignant cases.
Immunohistochemistry
Positive Markers:
Epithelial component: CK7+, CK8/18+, p63+ (myoepithelial cells)
Stromal component: vimentin+, CD34 variable, smooth muscle actin in some cells
p53 in malignant cases.
Negative Markers:
Epithelial markers negative in stromal component
CK20 negative
Desmin typically negative in stroma
S-100 usually negative
Myogenin negative.
Diagnostic Utility:
CD34 helps distinguish from fibroadenoma (positive in FA, variable in PT)
p53 and Ki-67 higher in malignant phyllodes
Cytokeratins confirm epithelial component
Vimentin marks stroma.
Molecular Subtypes:
No established molecular subtypes
Stromal component may show features of various mesenchymal differentiations
Sarcomatous areas may express lineage-specific markers.
Molecular/Genetic
Genetic Mutations:
MED12 mutations in stromal component (similar to fibroadenoma)
TERT promoter mutations in malignant cases
TP53 mutations in high-grade lesions
CDKN2A/B deletions described.
Molecular Markers:
p53 overexpression in malignant cases
High Ki-67 in stromal component of malignant tumors
Rb pathway alterations
DNA copy number alterations in malignant cases.
Prognostic Significance:
Benign phyllodes excellent prognosis with complete excision
Malignant cases 10-20% metastatic potential
Recurrence risk higher with positive margins
Metastasis usually hematogenous.
Therapeutic Targets:
No specific targeted therapies established
Chemotherapy used for metastatic malignant phyllodes (sarcoma protocols)
Radiation therapy controversial for high-risk cases.
Differential Diagnosis
Similar Entities:
Fibroadenoma
Spindle cell lesions of breast
Primary breast sarcoma
Metaplastic carcinoma
Giant fibroadenoma
Juvenile fibroadenoma.
Distinguishing Features:
Fibroadenoma: lower stromal cellularity, CD34+, no leaflike architecture on cytology
Sarcoma: no epithelial component, monophasic pattern
Metaplastic carcinoma: epithelial markers in spindle cells.
Diagnostic Challenges:
Cytological distinction from fibroadenoma challenging
Requires assessment of stromal cellularity and atypia
Sampling bias may miss diagnostic areas
Borderline cases difficult to classify.
Rare Variants:
Phyllodes tumor with liposarcomatous differentiation
Adenosarcoma-like phyllodes
Phyllodes tumor with osteosarcomatous elements
Malignant phyllodes with rhabdomyosarcomatous differentiation.
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.
Site and Procedure
Site: [breast location], Procedure: Fine needle aspiration cytology
Adequacy
Adequate for evaluation
Cellularity
Moderate to high cellularity
Pattern
Biphasic pattern with epithelial and stromal components
Epithelial Component
Cohesive clusters of benign ductal epithelial cells with myoepithelial cells
Stromal Component
Hypercellular stroma with spindle cells showing [mild/moderate/marked] atypia
Nuclear Features
Stromal cells show [bland/atypical] nuclear morphology with [rare/frequent] mitoses
Background
Clean background with minimal inflammatory cells
Cytological Diagnosis
Fibroepithelial lesion, favor phyllodes tumor - requires histological grading (Category IV)
Recommendation
Core biopsy or excision recommended for definitive diagnosis and grading