Pathology of mixed Müllerian tumours.

The term 'mixed Müllerian tumour' applies to uterine tumours composed of epithelial and mesenchymal elements of Müllerian origin. These neoplasms are classified into adenomyomas, adenofibromas, adenosarcomas, and carcinosarcomas (malignant Müllerian mixed tumours) based on whether the epithelial and stromal elements are benign or malignant. The rare atypical polypoid adenomyoma usually involves the lower uterine segment and, on curettings, may be confused with invasive adenocarcinoma. Adenosarcomas are low-grade neoplasms classified halfway along the spectrum of mixed Müllerian tumours, with adenofibromas at one end and carcinosarcomas (malignant Müllerian mixed tumours) at the other. Some tumours currently classified as 'adenofibromas' on the basis of their low mitotic count and lack of nuclear atypia are, in fact, well differentiated adenosarcomas. Carcinosarcoma is composed of admixed but distinctive carcinomatous and sarcomatous elements. On the basis of the clonal origin of both tumour components, carcinosarcomas are currently thought to be metaplastic carcinomas rather than uterine sarcomas.