[851] Diagnostic Utility of Antibody to Smoothelin in the Recognition of Muscularis Propria (MP) in Transurethral Resection of Urinary Bladder Tumor (TURBT) Specimens

GP Paner, JG Brown, S Lapetino, N Nese, R Gupta, SS Shen, MB Amin. Loyola University Medical Center, Maywood, IL; Cedars-Sinai Medical Center, Los Angeles, CA

Background: Accurate recognition of MP invasion by urothelial carcinoma is vital as it is a crossroad between conservative and aggressive management. Recently there has been attention to the hyperplastic pattern of MM which can mimic the MP. We have previously shown that smoothelin, a marker of terminally differentiated smooth muscle, is relatively specific for MP (positive staining) and is variably negative to weak in MM. The study was based on cystectomy specimen slides in which bladder cancer was not present. Pathologic staging in TURBT specimens is complicated by limited, unoriented, or highly cauterized samples. Herein, we test the capability of smoothelin in recognizing MP in TURBT specimens to substantiate its diagnostic applicability in routine practice.
Design: Representative sections from 70 TURBTs were immunostained with smoothelin (R4A; 1:150 dilution). MP was evaluated in H&E slides and the corresponding smoothelin immunohistochemistry (IHC) slides in a double blinded fashion. Smoothelin IHC staining was graded as 0 to +3.
Results: In 31/70 (44%) cases MP was involved by invasive carcinoma. Cautery artifact was present in 46/70 (66%) cases in variable amounts and IHC staining in MP was retained in its presence. 48/70 (69%) cases had MP by H&E microscopy and 48/70 (69%) cases had MP by smoothelin IHC based on 2+ or 3+ positivity in muscle bundles with round regular contour. Desmoplastic response to invasive carcinoma stained negatively for smoothelin. Retrospective analysis of morphology in 2 discrepant cases indicated the presence of cauterized MP in 1 case that was not originally identified. While in one case, MP recognizable on morphology was not detected by smoothelin. The sensitivity, specificity, positive predictive value and negative predictive value of smoothelin based on comparison with morphology in TURBT specimens was 97.9%, 95.2%, 97.9%, and 90.5%, respectively.
Conclusions: This study confirms the relatively high sensitivity and specificity for smoothelin in MP muscle including in TURBT specimens. Immunoreactivity is retained in the background of thermal tissue injury and involvement by carcinoma. Our data confirm the utility of smoothelin IHC in the accurate recognition of MP from MM or desmoplastic tumor reactions, thereby facilitating appropriate pathologic stage designation in often challenging TURBT specimens.
Category: Genitourinary (including renal tumors)

Monday, March 9, 2009 8:30 AM

Platform Session: Section A, Monday Morning