Interobserver agreement and the role of smoothelin immunostain in the evaluation of Muscularis Propria (MP) invasion of Bladder Urothelial Carcinoma (BUC)

Abstract

Link of Video Abstract: https://youtu.be/KymxBUAr9eIBackground: Bladder Urothelial Carcinoma (BUC) is common cancer in the genitourinary organs. One important determinant for its therapy modality is the presence of tumor invasion into Muscularis Propria (MP). Assessing MP invasion in routine Hematoxylin-Eosin (HE) slides of Transurethral Resection of Bladder (TUR-B) specimens is not always easy due to tissue fragmentation and morphological similarities of MP to muscularis mucosa (MM) and myofibroblasts. This study was done to determine the interobserver agreement in evaluating MP invasion and to find alternatives to overcome this diagnostic problem. Methods: This cross-sectional observational analytic study was conducted in the Pathology Laboratory of the Faculty of Medicine, Universitas Udayana/Prof. Dr. I.G.N.G. Ngoerah Hospital, Bali, in 2022. As many as 72 HE slides of TUR-B specimens of BUC patients were examined separately by five experienced pathologists. Smoothelin immunostaining, a marker to identify MP, was also examined as a comparison. Data were processed and statistically tested using the SPSS version 20.0 program for Windows. Results: The interobserver agreement of those five pathologists was found to be low to moderate, with an average = 0.48, ranging between 0.18-0.69. One pathologist had a low agreement with four others (<0.4) and indicated diagnostic uncertainty in 41% of the samples examined. Among four other pathologists, the agreements were moderate, with  = 0.40-0.69. The proportion of concordant examination results was only 45.8%. When the outcome of each HE slide was concluded by consensus, it was found that there was no statistically significant difference with smoothelin immunostaining results. Conclusion: Evaluation of MP invasion of BUC in TUR-B specimens had low to moderate interobserver agreement, which indicated that this examination was subjective. However, the consensus of several pathologists seems to lead to better accuracy, close to the result of smoothelin immunostaining.