Histogenesis of ovarian malignant mixed mesodermal tumours.

The histogenesis of ovarian malignant mixed mesodermal tumours, which includes the concept of metaplastic carcinoma, is controversial. Four such tumours were examined for evidence of metaplastic transition from carcinoma to sarcoma using morphology and reticulin stains. Consecutive sections were stained immunohistochemically using cytokeratin and vimentin to determine whether cells at the interface between carcinoma and sarcoma expressed both cytokeratin and vimentin. There was no evidence of morphological, architectural, or immunohistochemical transitions from carcinoma to sarcoma in the four tumours studied. This suggests that ovarian malignant mixed mesodermal tumours are not metaplastic carcinomas but are composed of histogenetically different elements.