Semiquantitative Smoothelin Expression in Detection of Muscle Invasion in Transurethral Resection and Cystectomy Specimens in Cases of Urinary Bladder Carcinoma

Objectives: To examine the usefulness of smoothelin - a new immunohistochemical (IHC) marker that is expressed predominantly in visceral smooth muscle - in recognizing muscularis propria (MP) in transurethral resection (TUR) and matched cystectomy specimens and to compare thepattern of its expression in muscularis mucosae (MM) and MP in radical cystectomy specimens. Methods: IHC staining for smoothelin was performed in 49 cases of urothelial carcinoma removed by radical cystectomy (16 had undergone TUR before the cystectomy). Results: In cystectomy specimens, smoothelin staining in the MP was strong (+3), moderate (+2) and weak (+1) in 49%, 44.9% and 6.1% of cases, respectively, whereas smoothelin positivity in the MM was absent and weak in 77.6% and 22.4% of cases, respectively. In TUR specimens, smoothelin immunoreactivity was moderate to strong in 68.8% and weak in 6.3% of cases and all of them proved to have MP invasion in cystectomy specimens. Conclusion: Smoothelin is a useful marker for the detection of MP in TUR specimens. Moderate to strong smoothelin staining of the muscles included in TUR specimens and split by the tumor is a sign of MP invasion. It may be useful in cancer staging and treatment decision making.