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Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 4 December 2011, last major update November 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● Marker of terminally differentiated smooth muscle cells, first described in 1996 (J Cell Biol 1996;134:401)


● Distinction of cytoplasmic from nuclear staining may be important

Uses by Pathologists

● In urothelial carcinoma, may help distinguish invasion of muscularis propria (positive) from muscularis mucosa (weak/negative, Am J Surg Pathol 2010;34:792, Am J Surg Pathol 2009;33:91), but there may be overlap of staining between the two layers (Virchows Arch 2011;458:665, Am J Surg Pathol 2010;34:418)
● In esophagus, stains weaker in neuromuscularis mucosa, but may need for both layers to be present simultaneously to accurately interpret depth of invasion (Am J Surg Pathol 2011;35:55)

Micro images

Various images

Positive staining - normal

● Differentiated smooth muscle cells

Positive staining - disease

● Cytoplasmic staining: benign smooth muscle tumors, GI leiomyosarcomas (24%, Am J Surg Pathol 2009;33:1795)
● Nuclear staining: GI leiomyosarcomas (41%), GIST (22%)

Negative staining

● Striated muscle, myofibroblasts, myoepithelial cells, pericytes
● Negative cytoplasmic staining in dedifferentiated liposarcoma, desmoid tumor, GIST, inflammatory myofibroblastic tumor, MPNST, schwannoma

End of Stains > Smoothelin

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