Adenomyoepithelioma of the Breast
Differential Diagnosis
- Various processes with cytologically atypical myoepithelial cells
- Myoid hamartoma
- Pleomorphic Adenoma
- Low Grade Adenosquamous Carcinoma
- Papilloma with Prominent Myoepithelial Cells
- Ductal Adenoma
- Metaplastic Carcinoma
- Myofibroblastoma
Various processes may have prominent atypical myoepithelial cells
- Cytologic atypia, increased mitotic rate, stromal invasion are not permitted in adenomyoepithelioma
- Such cases should be diagnosed based on the malignant component present
- Some such cases have been designated as "solid pattern adenomyoepithelioma" (Tavassoli 1991)
- We do not use that terminology
| Adenomyoepithelioma | Myoid Hamartoma |
|---|---|
| Myoepithelial component positive for keratin, p63, smooth muscle actin | Myoid component positive only for smooth muscle actin |
| Tubules without lobules | Well formed ducts and lobules |
| No admixed fat | Admixed fat |
| Pleomorphic Adenoma | Adenomyoepithelioma |
|---|---|
| Chondromyxoid stroma | Lacks chondromyxoid stroma |
| Low Grade Adenosquamous Carcinoma | Adenomyoepithelioma |
|---|---|
| Squamous differentiation frequent | Squamous differentiation not described |
| Infiltrative pattern | Circumscribed, not infiltrative |
| Papilloma with Prominent Myoepithelial Cells | Adenomyoepithelioma |
|---|---|
| Myoepithelial cells restricted to basal layer on papillae | Prominent, expanded myoepithelial component forming nodules or nests |
| Ductal Adenoma | Adenomyoepithelioma |
|---|---|
| Hyalinized stroma | Cellular stroma |
| Circumscribed, encapsulated | Capsule unusual |
| Metaplastic Carcinoma | Adenomyoepithelioma |
|---|---|
| Glandular component, if present, is histologically malignant, except in low grade spindle cell metaplastic carcinoma | Epithelial component is histologically bland |
| Stromal component may be bland or histologically malignant | Stroma is histologically bland |
| Stromal component may resemble a variety of sarcomas or low grade fibrous proliferation | Stroma shows myoepithelial differentiation only |
| Squamous differentiation may be present | No squamous differentiation |
| Myofibroblastoma | Adenomyoepithelioma |
|---|---|
| No epithelial component | Tubules integral to lesion |
| Stromal keratin negative, CD34 positive, muscle/myoid markers variable | Stromal keratin variable, p63 and muscle/myoid markers positive |
