Achaete-scute complex-like 1 (ASCL1), also called mammalian or human achaete-scute complex homolog-1 (MASH1, HASH1), is a basic helix-loop-helix transcription factor crucial for neuroendocrine cell differentiation.  Mash1 is important in the development of the brain and the diffuse neuroendocrine system including adrenal medullary chromaffin cells, ganglion cells, thyroid parafollicular C cells and pulmonary neuroendocrine cells1,2.

Immunohistochemical expression

Expression is nuclear.

  Pulmonary small cell carcinoma 49/591, 20/233    
Merkel cell carcinoma 0/301
Pulmonary squamous cell carcinoma 0/53  
Pulmonary large cell carcinoma 0/123  
Pulmonary large cell neuroendocrine carcinoma 10/173  
Pulmonary carcinoid 0/93  

Staining of small cell carcinoma tends to be lost if the tumour is crushed1.

Diagnostic utility


1 Ralston J, Chiriboga L, Nonaka D. MASH1: a useful marker in differentiating pulmonary small cell carcinoma from Merkel cell carcinoma. Mod Pathol. 2008 Nov;21(11):1357-62. FULL TEXT

2 Jiang SX, Kameya T, Asamura H, Umezawa A, Sato Y, Shinada J, et al. hASH1 expression is closely correlated with endocrine phenotype and differentiation extent in pulmonary neuroendocrine tumors. Mod Pathol. 2004 Feb;17(2):222-9.

3 Hiroshima K, Iyoda A, Shida T, Shibuya K, Iizasa T, Kishi H, et al. Distinction of pulmonary large cell neuroendocrine carcinoma from small cell lung carcinoma: a morphological, immunohistochemical, and molecular analysis. Mod Pathol. 2006 Oct;19(10):1358-68.

This page last revised 31.1.2010.

©SMUHT/PW Bishop