[638] Immunohistochemical Staining for Smoothelin Differentiates the Duplicated Muscularis Mucosa of Barrett's Esophagus from the True Muscularis Mucosa

HF Faragalla, CJ Streutker. University of Toronto, Toronto, ON, Canada; Saint Micheal Hospital, Toronto, ON, Canada

Background: The muscularis mucosa underlying the metaplastic mucosa of Barrett's esophagus is frequently duplicated, with an intervening layer of lamina propria between the superficial muscle layer (neo-muscularis mucosa, NMM) and deep muscularis mucosa (true muscularis mucosa, TMM). This duplication causes difficulties with accurate staging of superficially invasive carcinoma in biopsy specimens and endoscopic mucosal resections (EMR), as invasion underneath the superficial muscle layers may be mistaken for submucosal invasion. Intramucosal carcinoma (pT1a) can often be treated by EMR resection or other non-surgical modalities, whereas patients with submucosal (pT1b) invasion are recommended for esophagectomy. Therefore, the accurate staging of such specimens is crucial. Smoothelin is a novel smooth muscle protein expressed only by fully differentiated smooth muscle cells and not by proliferative or noncontractile smooth muscle cells and fibroblasts: it has been suggested that in the bladder it can separate hyperplastic muscularis mucosa from the true muscularis propria. We hypothesized that immunohistochemistry for smoothelin would differentiate the NMM from the TMM.
Design: Eleven cases of endoscopic mucosal resections for Barrett's related neoplasia were retrieved from the archives of the pathology department. Immunohistochemical staining for smoothelin, smooth muscle actin and smooth muscle myosin were performed to evaluate differential staining in the TMM versus NMM. The staining score was evaluated as follows: 0 < 5% of cells staining, +1 or focal =5%-10%, +2 or moderate =11% to 50%, +3 or strong, diffuse >50% muscle cell positivity.
Results: With SMA, strong and diffuse staining(+3) was observed with similar intensity and pattern in NMM(11/11) and TMM (11/11).With smoothelin, the NMM showed weak focal staining (+1) in 8/11 cases (73%), and moderate staining +2 in 3/11 cases (17%), and the TMM showed very strong and diffuse staining(+3) in 11/11cases (100%). With smooth muscle myosin, strong and diffuse staining was observed with similar intensity in both the TMM and NMM in 11/11 cases.
Conclusions: In our study, smoothelin staining in the NMM is significantly weaker than that seen in the true/deep muscularis mucosa. This suggests that this antibody may be of use in evaluation of esophageal biopsies or endoscopic resections to more accurately stage early stage adenocarcinomas.
Category: Gastrointestinal

Monday, March 22, 2010 1:00 PM

Poster Session II # 70, Monday Afternoon


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