Stains & molecular markers
Actin, alpha smooth muscle type

Topic Completed: 1 November 2013

Minor changes: 15 September 2020

Copyright: 2003-2020,, Inc.

PubMed Search: alpha smooth muscle actin[title]

Gina Johnson, M.D.
Page views in 2019: 10,357
Page views in 2020 to date: 8,443
Cite this page: Johnson G. Actin, alpha smooth muscle type. website. Accessed September 23rd, 2020.
Definition / general
  • Discovered in 1986 (J Cell Biol 1986;103:2787)
  • Antibodies to alpha smooth muscle actin do not detect the other actin isoforms
  • Also called smooth muscle actin, SMA; clone 1A4 or sm-1
Clinical features
  • Membranous or cytoplasmic staining
Uses by pathologists
Microscopic (histologic) images

Cases #92, 84 and 32

Leiomyosarcoma: cervix

Sinonasal hemangio-

Kidney atypical epithelioid angiomyolipoma

Images hosted on other servers:

Ameloblastic carcinoma

Bladder: PEComa

Breast: leiomyoma

Colon carcinosarcoma

Colon and small intestine: normal and intestinal pseudoobstruction

Eye: MFH of conjunctiva (top left)

Heart: fetus with heart block

Heart scar tissue

Leiomyosarcoma: bladder (fig C)

Lung: COPD

Myofibroblastic sarcoma
(left: smooth muscle actin,
right MIB-1)

Normal: breast myoepithelial cell disruptions

Normal: breast myoepithelial cells

Normal: decidual stromal cells

Normal: eye choroid and sclera

Plexiform fibrohistiocytic tumor

Pleomorphic sarcoma / MFH

Normal: liver (fetal)

Salivary gland sialometaplasia in parotid node

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

Positive staining - normal
Positive staining - disease
Negative staining
Normal tissue:

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