A hysterectomy specimen shows a bulky uterine tumour with admixed malignant epithelial glands and malignant stromal elements containing cartilage and skeletal muscle. Immunohistochemistry shows both components share identical p53 mutations. How is this tumour currently classified by the WHO?

• A A benign phyllodes-like lesion of the endometrial stroma
• B Low-grade endometrial stromal sarcoma with glandular elements
• C Adenosarcoma with sarcomatous overgrowth
• D Metaplastic carcinoma of the endometrium (carcinosarcoma) ✓

Explanation

Malignant mixed Mullerian tumour, now termed carcinosarcoma, is classified by current WHO criteria as a metaplastic variant of endometrial carcinoma rather than a true sarcoma. Clonal analysis and shared molecular alterations such as identical p53 mutations demonstrate that both epithelial and sarcomatous components derive from a single carcinoma clone undergoing mesenchymal metaplasia. Adenosarcoma has benign glands with malignant stroma, and endometrial stromal sarcoma lacks malignant epithelium, so neither fits.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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