Novel markers of squamous differentiation in the urinary bladder

Summary Urinary bladder squamous cell carcinoma and urothelial carcinoma with squamous differentiation are often high-grade and high-stage tumors that are thought to be associated with a poorer prognosis and response to therapy compared with urothelial carcinoma without divergent differentiation. Therefore, recognition of a squamous component is increasingly important in guiding prognosis and therapy. We investigated the expression of MAC387, desmoglein-3, and TRIM29 in pure squamous cell carcinoma and urothelial carcinoma with squamous differentiation to determine whether they have utility as diagnostic biomarkers for squamous differentiation. Eighty-four cases were retrieved from participating institutions including 51 pure urinary bladder squamous cell carcinomas and 33 urothelial carcinomas with squamous differentiation. MAC387, desmoglein-3, and TRIM29 antibodies demonstrated positive staining in pure squamous cell carcinoma in 51 (100%), 46 (90%), and 48 (93%) cases, respectively. Urothelial carcinoma with squamous differentiation showed reactivity for MAC387, desmoglein-3, and TRIM29 in the squamous component for 32 (97%), 26 (79%), and 32 (97%) cases, respectively. MAC387 demonstrated a sensitivity of 99% and a specificity of 70% for squamous differentiation, whereas desmoglein-3 yielded a sensitivity of 86% and a specificity of 91%. No urothelial component showed greater than 10% labeling for desmoglein-3. TRIM29 labeling showed a sensitivity of 95%, but a poorer specificity of 33%. In summary, MAC387 and desmoglein-3 are reliable diagnostic markers for supporting the morphologic impression of squamous differentiation in urinary bladder carcinoma. Desmoglein-3 shows high specificity, whereas TRIM29 was most likely to demonstrate labeling in areas without light microscopically recognizable squamous differentiation.