Does desmin immunohistochemistry have a role in assessing stage of urothelial carcinoma in transurethral resection of bladder tumor specimens?

Context: Pathological stage is the most important determinant of clinical outcome of bladder carcinoma patients. pT 1 carcinoma is defined by invasion into lamina propria, including muscularis mucosae ( MM), but not into muscularis propria (MP) (pT 2). However, pathological staging of the tumor is a complicated task for pathologists. "Splitting of MP" or "hypertrophy of MM" caused by tumor invasion are important causes of interpretation subjectivity leading to intra-pathologist variation and disagreement. The aim of the study was to prospectively evaluate the utility of desmin immunohistochemical expression for evaluation of muscle invasion in transurethral resection of bladder tumor (TURBT) specimens. Materials and Methods: A total of 40 TURBT cases was taken. Specimens were processed, stained with H and E, graded and evaluated to determine whether MP invasion was present. Desmin immunohistochemistry (IHC) was used to assess muscle invasion and compare the result with H and E stained sections. Tumors with radiological evidence of gross invasion and those of stage T is were excluded. Results: Among 40 TURBT cases, there were 37 cases of transitional cell carcinoma. Among them, 17 were high grade and 20 were low grade. On H and E, 17/37 cases showed MP invasion, 8/37 cases showed no MP invasion and the rest 12/37 had questionable MP invasion. Desmin staining intensity was graded from 0 to 3+. MM showed negative (0) and moderate (2+) staining in one case each, mainly (35/37) showed mild (1+) staining intensity. MP showed moderate (2+) (3/37) to strong (3+) (34/37) staining intensity. Among 12/37 questionable cases (on H and E) desmin staining showed definite MP invasion in eight cases. Conclusions: Although morphology remains the gold standard, desmin IHC has diagnostic utility in the evaluation of questionable MP invasion and hence in staging of urothelial carcinoma.