Smoothelin immunohistochemistry is a useful adjunct for assessing muscularis propria invasion in bladder carcinoma.

AIMS

To prospectively evaluate the utility of smoothelin immunohistochemical expression for the evaluation of muscularis propria (MP) in diagnostic transurethral resection of bladder tumour (TURBT) specimens and cystectomies.

METHODS AND RESULTS

Smoothelin immunohistochemistry was performed on a total of 26 TURBT and cystectomy specimens. All but two cases (24/26) demonstrated strong (3+) or moderate (2+) immunoreactivity of the MP with smoothelin. Muscularis mucosae (MM) never displayed strong (3+) reactivity, and in only one case did the MM have moderate (2+) reactivity; in this case the MP had strong (3+) reactivity. MM intensity mirrored the intensity of reactivity of blood vessels in all cases (26/26). Using moderate or strong immunoreactivity as a cut-off, smoothelin had a sensitivity of 92% for detecting MP and a specificity of 97% for distinguishing between MP and MM. In all unequivocal MP-invasive and lamina proporia-invasive cases by haematoxylin and eosin (H&E), smoothelin immunohistochemistry confirmed the original light microscopic diagnosis. In four cases in which there was equivocal MP involvement by H&E, smoothelin helped establish MP invasion.

CONCLUSIONS

Smoothelin immunohistochemistry has diagnostic utility in the evaluation of MP invasion in urothelial carcinoma. Smoothelin could be used as an adjunct to traditional H&E-stained light microscopy and may help reduce the number of equivocal diagnoses.