Retroperitoneal LM may have mitosis (but not >5/HPF).
Immunohistochemistry: actin+, desmin+.
True LMs are benign lesions that merely require excision with a small cuff of normal tissue.
DDX: Other spindle cell tumors that are low-grade appearing.
Schwannoma: wavy nuclei, hypo and hypercellular areas, Verocay bodies and S100+, actin-
GIST: related to bowel wall, perinuclear vacoulations; CD117+, DOG1+.