 There is debate over the naming of MMMT; the term carcinosarcoma was formerly used to describe lesions with homologous tumors, and "malignant mixed Müllerian tumor" or "mixed mesodermal tumor" was used to describe heterologous tumors.While "carcinosarcoma" now considered standard, "malignant mixed Müllerian tumor" has a lengthy history within gynecological literature and is expected to continue to be used.The naming issue to a certain extent reflects histological characteristics and development of the tumors, in which the different types of tissues are believed to either develop separately and join into a single mass (the "collision" theory), that an adenocarcinoma stimulates the stroma to create a tumor (the "composition" theory), or that the tumor is the result of a stem cell that differentiates into different cell types (the "combination" theory).