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Correlation between Alcian blue–periodic acid–Schiff stain and immunohistochemical expression of mucin 2 in Barrett's oesophagus

Sir: Barrett’s oesophagus (BO) is an acquired condition in which a length of the oesophageal squamous epithelium is replaced by a columnar epithelium containing goblet cells. It appears in up to 2% of the general population submitted to oesophagogastroduodenoscopy and 10% of patients with chronic symptoms of gastro-oesophageal reflux. The annual incidence of adenocarcinoma in this epithelium ranges between 0.2% and 2.1% in patients without dysplasia and up to 70% in those with high-grade dysplasia with a follow-up of 1–9 years. Therefore, an adequate diagnosis of BO is very important. In this regard, the Alcian blue– periodic acid–Schiff (AB–PAS) stain is helpful in the identification of intestinal metaplasia. Despite its usefulness, however, this technique is labourious, time-consuming, and more expensive than haematoxylin and eosin (H–E) staining. Indeed, AB–PAS may present difficulties of interpretation due to its heterogeneous staining. The biochemical marker of cellular differentiation mucin 2 (MUC-2) is able to identify intestinal metaplasia and represents a promising method for correlation with histopathological findings. We investigated whether MUC-2 is a good substitute for AB–PAS in the detection of goblet cells. Biopsy specimens from 40 BO patients were stained with H–E and AB–PAS. The expression of MUC-2 was evaluated by streptavidin–biotin peroxidase technique. The primary antibody was the mouse monoclonal antibody against MUC-2 (Ccp58; Novocastra Laboratories, Newcastle, UK). The secondary antibody was the antimouse rabbit of Dako LSAB 2 System kit (K0675; Dako Corp., Carpinteria, CA, USA). The chromogen used was DAB. Slide interpretation was carried out blindly by two examiners using a light microscope. The intraand interobserver agreements on the expression of MUC-2 in AB–PAS+ cases were determined by j statistics. MUC-2 showed expression in goblet cells and occasional expression in columnar cells, but was not expressed in either cardiac mucosa or in submucosal glands (Figure 1). There was full agreement between MUC-2 expression and staining of goblet cells by AB–PAS (Figure 2), with all patients showing a positive reaction with the use of either technique. In conclusion, MUC-2 expression turned out to be a helpful tool for the correct identification of intestinal metaplasia, avoiding any false-negatives or even false-positive results that may occur with the use of AB–PAS staining. These findings warrant the use of MUC-2 in the histopathological diagnosis of Barrett’s oesophagus.