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WHO Classification of Tumours
Metaplastic carcinoma, NOS


A general term used to describe carcinomas arising from epithelial cells that have been transformed into another cell type (metaplastic epithelial cells). The term is also used to describe carcinomas in which the malignant epithelial cells show differentiation towards another cell type.

Metaplastic breast carcinoma is characterized by malignant glandular cells showing squamous, spindle cell, or chondroid/osseous differentiation. It is a rare tumour (<1% of all invasive breast carcinomas). Patients are on average 55 years old at presentation. They typically present with a well circumscribed, firm, palpable lump (median size 3-4 cm, but lesions >20 cm have been described)

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Tavassoli FA, Devilee P (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs.
3rd Edition
IARC Press: Lyon 2003


The following subtypes are recognized:

> Pure epithelial metaplastic carcinomas are composed entirely of metaplastic cells without any recognizable admixture of adenocarcinoma.
- Squamous cell carcinoma
- Adenocarcinoma with spindle cell metaplasia
- Adenosquamous carcinoma
- Mucoepidermoid carcinoma

> Mixed epithelial/mesenchymal metaplastic carcinomas are composed of infiltrating carcinoma mixed with mesenchymal elements.
- Adenocarcinoma with cartilaginous and osseous metaplasia
- Carcinosarcoma
- Matrix producing carcinoma