With regard to the malignant behavior of leimyosarcoma, the most impoant criterion is:
Blood vessel penetration by tumor cells
Tumor cells in lymphatic channels
Lymphocyte infiltration
The number of mitoses per high power field
An impoant microscopic criterion for distinguishing leiomyosarcoma from leiomyoma is the number of mitoses present. Greater than 10 mitoses per10 high-power fields (hpf) is associated with frank malignancy (leiomyosarcoma). Ref: Robbin's Basics of Pathology , 7th Edition, Page I090; Oncology: An Evidence-Based Approach By Alfred E. Chang, 2006, Page 944.