Table 3.

Applications of alpha smooth muscle actin (SMA) in the diagnosis of soft tissue tumors and findings that should be taken into account in differential diagnosis

Benign myofibroblastic lesions (strongly positive)	Nodular fasciitis (typical, some are only weakly positive of even negative), fibroma of tendon sheath
	Reactive myofibroblastic proliferations (typically)
Myofibroblastic lesions (focally positive)	Desmoid fibromatosis, other fibromatoses
Inflammatory myofibro-blastic tumor	Variably positive (negative for extensively positive)
Leiomyoma/leiomyosarcoma	Virtually all cases are positive. If tumor is SMA negative, this is a reason to doubt a diagnosis of smooth muscle tumor
Gastrointestinal stromal tumor (GIST)	Approximately 1/3 of GISTs are variably SMA-positive, some strongly, as seen for smooth muscle tumors
Vascular tumors	Benign angiomas show retained pericytes
	Vasoformations in malignant vascular tumors typically lack pericytes
Myoepithelial cells/lesions	Normal myopeithelial cells are positive but myoepithelial neoplasms only focally positive or totally negative