How is uterine carcinosarcoma (malignant mixed Mullerian tumour) classified in current WHO and FIGO schemes?

• A A variant of uterine sarcoma arising from endometrial stromal cells
• B A benign mixed tumour with malignant potential
• C A distinct entity intermediate between carcinoma and sarcoma with separate staging
• D A metaplastic high-grade endometrial carcinoma with epithelial and sarcomatous components ✓

Explanation

Immunophenotypic and molecular studies show that both components of carcinosarcoma share the same clonal origin from a single carcinoma precursor, usually carrying TP53 or PTEN alterations. It is therefore classified as a metaplastic high-grade endometrial carcinoma, not a true sarcoma, and it is staged using the endometrial carcinoma FIGO system. Its behaviour resembles high-grade serous carcinoma, with early peritoneal and nodal spread. The sarcomatous element may show heterologous differentiation such as cartilage or striated muscle.

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

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