It is characterized by a higher incidence of deep myometrial invasion, lymph-vascular space involvement, lymph node metastases, extrauterine disease, and positive peritoneal cytology and implants. UPSC resembles papillary serous carcinoma of the ovary histologically. Unfortunately, UPSC does not share the same response to cytotoxic agents as does its ovarian counterpart. In fact, neither radiation therapy nor chemotherapy has proven to be highly successful forms of adjuvant therapy for this histologic variant of endometrial carcinoma. Clear cell carcinoma is another variant of endometrial carcinoma characterized by its aggressive behavior.
Nuclear grade adds no prognostic information in terms of survival.
The diagnosis of LMS vs. leiomyoma and leiomyoma with high mitotic activity or uncertain malignant potential is based on the metastatic potential of the tumor. The mitotic count and cellular atypia correlates to this metastatic potential. There are some who believe mitotic count alone is not a good indicator of metastatic potential. The sarcomatous portion of the tumor may exhibit an ESS pattern, if differentiated. MMTs are termed heterologous only if identifiable extrauterine histology is demonstrated.