Actin, alpha smooth muscle type

Author: Gina Johnson, M.D. (see Authors page)

Revised: 23 September 2015, last major update November 2013

Copyright: (c) 2003-2015,, Inc.

PubMed Search: alpha smooth muscle actin[title]
  • 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
Micro Images

Normal: breast myoepithelial cell disruptions

Normal: breast myoepithelial cells

Normal: decidual stromal cells

Normal: eye choroid and sclera

Normal: liver (fetal)

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

Breast: leiomyoma

Breast: fibromatosis

Breast: hamartomas-myoid

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

Colon and small intestine: normal and intestinal pseudoobstruction

Crohn disease: obliterative muscularization

Eye: MFH of conjunctiva (top left)

Heart: fetus with heart block

Heart scar tissue

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

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

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

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

Lung: COPD

Lung: lymphangio-leiomyomatosis

Lung: adenocarcinoma, subepithelial myofibroblasts

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

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


Placenta accreta (fig 3)

Plexiform fibrohistiocytic tumor

Pleomorphic sarcoma / MFH

Salivary gland duct carcinoma

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
Positive Staining - Disease
Negative Staining
Normal tissue: