Phyllodes Tumor of the Breast
Differential Diagnosis
The histologic border between these two is not always sharp
| Juvenile Fibroadenoma |
High Grade Phyllodes Tumor |
| No stromal atypia |
Atypical stroma |
| Stromal mitotic rate < 3/10 hpf |
Elevated stromal mitotic rate |
| No stromal overgrowth |
Stromal overgrowth |
| Does not infiltrate |
May infiltrate surrounding breast |
Stromal overgrowth defined as at least one low power field (40x total magnification) composed entirely of stroma
| Fibroadenoma |
Low Grade Phyllodes Tumor |
| Lacks significant stromal hypercellularity |
Hypercellular stroma is prominent |
| No stromal overgrowth |
May have stromal overgrowth |
| No leaf-like architecture |
Prominent leaf-like architecture |
| No condensation around ducts |
Stromal condensation around ducts |
| Does not infiltrate |
May infiltrate surrounding breast |
The histologic border between these two is not always sharp
| Metaplastic Carcinoma |
Phyllodes Tumor |
| Spindled component may be positive for high molecular weight keratin or p63 |
Stromal component negative for high molecular weight keratin and p63 |
| Epithelial component is malignant |
Epithelial component is benign |
| Squamous differentiation may be present |
No squamous differentiation |
Pure Sarcoma of the Breast
- Very rare
- The presence of an epithelial component defines phyllodes tumor
Fibromatosis
- Bland spindle cells
- Stellate configuration
- Absence of intrinsic epithelial component
- May entrap normal breast lobules
Myofibroblastoma
- Resembles solitary fibrous tumor
- Lacks intrinsic epithelial component
