Metaplastic Carcinoma of the Breast
Definition
- Breast carcinoma exhibiting either a mesenchymal (or other non-epithelial) component or squamous differentiation
Alternate / Historical Names
- Adenosquamous carcinoma
- Carcinosarcoma
- Matrix producing carcinoma
- Sarcomatoid carcinoma
- Spindle cell carcinoma
- Squamous cell carcinoma
Diagnostic Criteria
- Must have a neoplastic component that is either squamous or non-epithelial
- Carcinoma mixed with a mesenchymal or other non-epithelial component
- May exhibit obviously malignant stroma
- May resemble pleomorphic MFH or fibrosarcoma
- May exhibit heterologous differentiation
- Usually osteosarcoma or chondrosarcoma
- Less commonly glioma, melanoma, rhabdomyosarcoma, angiosarcoma or liposarcoma
- Stroma may be composed of bland spindle cells (spindle cell carcinoma)
- p63 positive, often high molecular weight keratin positive
- May contain fibroblasts and or myofibroblasts
- May resemble nodular fasciitis or fibromatosis
- Mesenchymal component may be keratin positive in about half of cases
- High molecular weight keratin is most often positive
- Epithelial component may be sparse
- May be identified only by presence of keratin reactivity
- Broad spectrum and high molecular weight keratins are useful
- Squamous component may be cystic
- Carcinomas with metaplastic squamous components
- Most have a component of ductal carcinoma
- There are rare reports of metaplastic carcinoma associated with lobular, medullary, mucinous and tubular carcinoma
