Stains - Actin, alpha smooth muscle type

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Stains

Actin, alpha smooth muscle type

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 14 December 2011, last major update December 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Discovered in 1986 (J Cell Biol 1986;103:2787)
● Antibodies to alpha smooth muscle actin do not detect the other actin isoforms

Terminology
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● Also called smooth muscle actin, SMA; clone 1A4 or sm-1

Clinical features
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● No apparent deficiency in intestinal pseudoobstruction (J Clin Pathol 2004;57:1168)
● May predict aggressive behavior in cutaneous basal cell carcinoma (Hum Pathol 2010;41:1128) and pancreatic ductal adenocarcinoma (Pancreas 2010 May 7 [Epub ahead of print])

Interpretation
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● Membranous or cytoplasmic staining

Uses by pathologists
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● Identify smooth muscle cells and myofibroblasts in normal, reactive (Am J Respir Cell Mol Biol 1999;20:582) or neoplastic tissue (Am J Dermatopathol 2006;28:105)
● Identify myoepithelial cells in normal, neoplastic or diseased breast, salivary glands or sweat glands; may be helpful to rule out invasion; may be particularly important in cytology specimens (Anticancer Res 2003;23:4175)
● Identify pericytes (Oncology 2005;69:159)
● Help distinguish pleuropulmonary desmoid tumors (SMA+) from solitary fibrous tumor (SMA-, Arch Pathol Lab Med 2006;130:1503)
● Note: in breast papillary lesions, p63 is more sensitive and specific because smooth muscle actin also stains stromal cells (J Clin Pathol 2007;60:315)

Micro images
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Normal: decidual stromal cells

Normal: eye choroid and sclera


Normal fetal liver


Ameloblastic carcinoma

Bladder - PEComa

Bone: glomus tumor

Breast: myoepithelial cells (fig C/G)

Breast: adenoid cystic carcinoma (fig B) vs collagenous spherulosis (fig G)

Breast: basal-like carcinoma (fig a)

Breast: cellular fibroadenoma (fig a-black cytoplasmic staining) and phyllodes tumor (fig b)

Breast: fibromatosis

Breast: hamartomas-myoid

Breast: leiomyoma

Breast: myoepithelial cell disruptions in normal and hyperplastic epithelium

Cardiac scar tissue


Colon (left to right): carcinosarcoma; leiomyoma (top); Peutz Jeghers polyp (fig 4)

Colon and small intestine: normal and intestinal pseudoobstruction

Crohn’s disease - obliterative muscularization

Eye: MFH of conjunctiva (top left)

Heart: fetus with heart block


Inflammatory myofibroblastic tumor (left to right): bone, gallbladder, salivary gland (fig 3b)


Kidney (left to right): atypical epithelioid angiomyolipoma (two images), focal segmental glomerulosclerosis

Larynx - spindle cell carcinoma (fig 1e)


Leiomyosarcoma (left to right): bladder (fig C), cervix, esophagus


Liver: left-epithelioid angiomyolipoma; right-glomangioma (fig 5)


Lung-normal and early pulmonary hypertension (left); late pulmonary hypertension (right)


Lung-COPD


Lung: left-lymphangioleiomyomatosis, right-desmoid tumor (fig D)


Lung adenocarcinoma-Subepithelial myofibroblasts

Melanoma - desmoplastic (fig 7)

Myofibroblastic sarcoma (left: smooth muscle actin, right: muscle specific actin)


Neuroblastoma

Placenta accreta (fig 3)

Plexiform fibrohistiocytic tumor (staining of tumor cells around nests)

Pleomorphic sarcoma / MFH

Salivary gland duct carcinoma - myoepithelial layer rules out invasion

Salivary gland sialometaplasia in parotid node

Sinonasal hemangiopericytoma


Stomach: left-gastric carcinoma-diffuse type (fig A); right-gastric carcinoma-intestinal type (fig A)

Submandibular gland - adenoid cystic carcinoma

Positive staining - normal
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● Breast myoepithelial cells (most, Breast Cancer Res 2003;5:R151)
● Salivary glands, sweat glands and tracheobronchial glands (J Histochem Cytochem 1988;36:659)
● Myofibroblasts (except alveolar - J Histochem Cytochem 1992;40:1955, and some granulation tissue / scars - Lab Invest 1989;60:275, Int J Legal Med 1992;105:99)
● Pericytes (J Histochem Cytochem 1989;37:315), smooth muscle and vascular smooth muscle
● Also chondrocytes (Folia Biol (Praha) 2006;52:167), choroidal non-vascular smooth muscle cells (J Anat 2005;207:381)
● Decidual stromal cells (Hum Reprod 1999;14:1599), fibroblastic reticulum cells (J Cancer Res Clin Oncol 1981;101:149)
● Glomus coccygeum (Arch Pathol Lab Med 1999;123:905), hepatic stellate cells (Virchows Arch 1997;430:195)
● Osteoblasts (J Orthop Res 2002;20:622)

Positive staining - disease
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● Adenoid cystic carcinoma (Arch Pathol Lab Med 1999;123:801)
● Angiomyofibroblastoma (occasionally focal, Hum Pathol 1997;28:1046)
● Angiomyolipoma
● Atypical teratoid / rhabdoid tumor (J Neurosurg 1996;85:56)
● Collagenous spherulosis (Mod Pathol 2006;19:1351)
● Endometrial stromal sarcoma (65%, Gynecol Oncol 2004;92:71)
● Endometriosis-stroma (Pathol Int 2003;53:371)
● Epithelial-myoepithelial carcinoma (Am J Surg Pathol 2007;31:44)
● Epithelioid sarcoma-proximal type (33%, Am J Surg Pathol 1997;21:130)
● Fibromatosis (56%, Am J Surg Pathol 2002;26:1296)
● Fibroblastic reticulum cell tumor (Am J Surg Pathol 1998;22:1048)
● Gastric carcinoma stromal cells (J Clin Pathol 2002;55:741)
● GIST (45%, Am J Surg Pathol 2002;26:1296)
● Glomus tumor (Hum Pathol 1999;30:1259)
● Granulosa cell tumors of ovary-adult (variable, Mod Pathol 1995;8:25)
● Hemangiopericytoma (Am J Surg Pathol 2003;27:737)
● Kidney-focal segmental glomerulosclerosis (Braz J Med Biol Res 2001;34:985)
● Inflammatory myofibroblastic tumor (Ann Diagn Pathol 2001;5:335, Am J Surg Pathol 1992;16:896)
● Leiomyoma
● Leiomyosarcoma
● Liposarcoma (focal in some cases, Am J Surg Pathol 2004;28:1257)
● Maligant fibrous histiocytoma (30%, J Clin Pathol 2003;56:666)
● Melanoma-desmoplastic (Am J Dermatopathol 1999;21:537)
● Mesothelioma-sarcomatoid (60%, Histopathology 2003;42:270)
● Myoepithelioma (57%, Hum Pathol 2004;35:14)
● Myofibroblastic sarcoma (Chin Med J (Engl) 2007;120:363)
● Nodular fasciitis (Ann Diagn Pathol 2002;6:94)
● Ossifying fibromyxoid tumor (some, J Laryngol Otol 1993;107:75)
● Pancreatic stellate cells post-obstruction (J Surg Res 2003;114:6)
● Plexiform fibrohistiocytic tumor (Histopathology 1991;19:503)
● Plexiform fibromyxoma (Am J Surg Pathol 2009;33:1624)
● Pulmonary lymphangioleiomyomatosis (J Clin Pathol 1993;46:479)
● Renal mixed epithelial and stromal tumor (Arch Pathol Lab Med 2006;130:80)
● Rhabdomyoma (focal / rare, Hum Pathol 1993;24:754, Hum Pathol 1993;24:608)
● Rhabdomyosarcoma (botryoid type, Pediatr Dev Pathol 2005;8:427)
● Spindle cell carcinoma (Am J Surg Pathol 2001;25:1009)
● Synovial sarcoma (25%, Mod Pathol 2007;20:760)

Negative staining - normal
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● Cardiac muscle (positive during development, J Cell Sci 2007;120:229)
● Skeletal muscle (J Cell Biol 1985;100:807)

Negative staining - disease
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● Carcinomas (usually)
● Myofibroblastoma (occasionally focally positive, Pathology 2005;37:144, Am J Surg Pathol 2001;25:1022)
● Schwannoma, solitary fibrous tumor (Arch Pathol Lab Med 2006;130:1503)

End of Stains > Actin, alpha smooth muscle

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