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Stains
Actin-muscle specific
Reviewer: Nat Pernick, M.D., PathologyOutlines.com, Inc. (see Reviewers page)
Revised: 27 April 2011, last major update April 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.
Definition
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● Recognizes all alpha actins (skeletal, smooth, cardiac) and gamma smooth muscle actin; but not beta cytoplasmic or gamma cytoplasmic actin (the latter is also called non-muscle actin)
● Recognizes actin expressed in all cells with muscle differentiation (cardiac, smooth and skeletal muscle), myoepithelial cells, myofibroblasts, pericytes and myogenic tumors
● Discovered in 1987 (Am J Pathol 1987;126:51)
Terminology
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● Also called HHF35, MSA
Uses
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(1) Identify skeletal muscle (Tumori 2007;93:198, J Cutan Pathol 2007;34:352) and smooth muscle cells (Eur Respir J 2001;17:316) in normal tissue or various disease entities
(2) Classify tumors with smooth or skeletal muscle, pericytes, myofibroblasts or myoepithelial cells
(3) Differentiate leiomyosarcoma (MSA+, keratin-) from spindle cell carcinoma (MSA-, keratin+, Am J Otolaryngol 2005;26:201)
Positive staining (normal)
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● Cardiac muscle, decidua, myoepithelial cells (although calponin and vimentin may be better, Braz Dent J 2007;18:192), myofibroblasts, pericytes, skeletal muscle, smooth muscle, vascular smooth muscle
Positive staining (disease)
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● Adenoid cystic carcinoma-myoepithelial component (J Oral Maxillofac Surg 2006;64:415), angiomyolipoma
● Cardiac rhabdomyoma, chondroblastoma (35%, Hum Pathol 1997;28:316)
● Endometriosis-smooth muscle (Hum Reprod 2000;15:767)
● Fibromatosis (Acta Cytol 1991;35:403)
● Glioblastoma multiforme (occasional), glomus tumor (Hum Pathol 1999;30:1259)
● Inflammatory myofibroblastic tumor (Mod Pathol 2001;14:784)
● Leiomyoma (Int J Gynecol Pathol 1995;14:134), leiomyosarcoma (80-100%, J Pak Med Assoc 2005;55:138, APMIS 1997;105:793)
● Malignant fibrous histiocytoma (30%, J Clin Pathol 2003;56:666), myoepithelioma, myofibroblastic sarcoma (Chin Med J (Engl) 2007;120:363), myofibroblastoma (variable), myopericytoma (Hum Pathol 2010;41:1500)
● Osteosarcoma (Am J Clin Pathol 2000;113:663)
● Pleomorphic adenoma (Hum Pathol 1991;22:1206)
● Rhabdomyosarcoma (but MyoD1 and myogenin are more specific/sensitive, Am J Surg Pathol 2006;30:962)
● Sinonasal-hemangiopericytoma (Head Neck 2005;27:124, Am J Surg Pathol 2003;27:737)
● Solitary fibrous tumor (variable staining, Mod Pathol 1997;10:443)
Negative staining
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● Angiomyofibroblastoma (Pathol Int 1995;45:487), mesothelioma-epithelioid (Am J Surg Pathol 2006;30:463)
Micro images
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Cardiac rhabdomyoma-highlights spider cells and cross striations (arrowheads)
Endometriosis
Hemangioma-outlines vascular channels (left: heart, right: lymph node)
Leiomyosarcoma-cervix
Myoepithelioma-breast
Myofibroblastic sarcoma (left: smooth muscle actin, right: muscle specific actin)
Prostate-sclerosing adenosis
Rhabdomyosarcoma (left: vagina (botyroides), middle: orbit,
Additional references
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End of Stains > Actin-muscle specific
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