SMA

See also : ACTA2

Expression

 smooth muscle tumors

• leiomyoma
• leiomyosarcoma

 bone tumors

• Alpha isoform of smooth muscle actin (SMA) expression has been reported in giant cell tumour of bone (GCTB) and other benign and malignant bone tumours.
• The nature of SMA-expressing cells in bone tumours is uncertain but they are negative for desmin and caldesmon and could represent either myofibroblasts or perivascular cells, such as pericytes.
• giant cell tumour of bone - GCTB
• aneurysmal bone cyst - ABC
• chondroblastoma - CB
• chondromyxoid fibroma
• " malignant fibrous histiocytoma " of bone (12401825)
  • MFH of bone may derive from mesenchymal stromal cells in bone marrow and has a more myofibroblastic differentiation than soft tissue MFH.

• osteosarcomas
  • ezrin -EZR and alpha-smooth muscle actin are predictive IHC prognostic markers for patients with an osteosarcoma. (17786474)

IHC marker for diagnosis

 SMA identifies smooth muscle cells and myofibroblasts in normal, reactive or neoplastic tissue. (Am J Respir Cell Mol Biol 1999;20:582)(Am J Dermatopathol 2006;28:105)

 SMA identifies myoepithelial cells in normal, neoplastic or diseased breast, salivary glands or sweat glands. (Anticancer Res 2003;23:4175)

• It may be helpful to rule out invasion.
• It may be particularly important in cytology specimens.

 SMA identifies pericytes to correlate with hematogenous metastasis and prognosis. (Oncology 2005;69:159)

 SMA can help distinguish pleuropulmonary desmoid tumors (SMA+) from solitary fibrous tumor (SMA-, Arch Pathol Lab Med 2006;130:1503).

 In breast papillary anomalies, p63 is more sensitive and specific because smooth muscle actin - SMA also stains stromal cells (J Clin Pathol 2007;60:315).