With regard to the malignant behavior of leiomyosarcoma, 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
Ans. is 'd' i.e., The number of mitoses per high power field The distinction of Leiomyosarcoma from Leiomyomas: It is based on the combination of: Degree of nuclear atypia Mitotic index Zonal Necrosis The most impoant single criteria is the number of nuclear mitoses present With or without Nuclear atypia (Independent of nuclear atypia) --> The presence of ten or more mitoses per ten high power (x400) fields indicates malignancy with or without cellular atypism. In presence of nuclear atypia or large cells --> If the tumor contains nuclear atypia or large epithelioid cells, five mitoses per ten high power fields are sufficient to justify a diagnosis of malignancy.