Evaluation of the relationship between adenosarcoma and carcinosarcoma and a hypothesis of the histogenesis of uterine sarcomas.

The terminology of uterine sarcomas is confusing and has been inconsistently applied. The relationships among the various types of uterine sarcomas are unknown. To elucidate the relationship between carcinosarcoma (malignant mullerian mixed tumor) and adenosarcoma, a series of 26 consecutive endometrial carcinosarcomas was evaluated for the presence of an adenosarcoma-like component. Four of 26 carcinosarcomas (15%) had an adenosarcoma-like component. The clinical and pathologic features of these tumors were otherwise similar to ordinary endometrial carcinosarcomas. A histogenetic schema for uterine sarcomas is proposed, interrelating endometrial stromal sarcomas, adenosarcomas with and without sarcomatous overgrowth, and poorly differentiated sarcoma not otherwise specified. Although most carcinosarcomas are accepted as being metaplastic or sarcomatoid carcinomas, it is suggested that the carcinomatous component of 8% to 16% of carcinosarcomas arise within, or in the endometrium adjacent to, an adenosarcoma. This latter group is then integrated into the histogenetic schema. Observations based on our data and the limited data in the literature that support this hypothesis include: 13% of endometrial carcinosarcomas have gross and microscopic features of collision tumors, 13% have an adenosarcoma-like component, 16% have a low-grade stroma, and approximately 8% are biclonal indicative of a collision tumor. The most parsimonious interpretation of these data indicates that approximately 8% to 16% of endometrial carcinosarcomas arise because of malignant transformation of the epithelial component within, or in the endometrium adjacent to an adenosarcoma.