Different immunohistochemical and ultrastructural phenotypes of squamous differentiation in bladder cancer

Abstract

Besides worse prognosis of bladder cancer with squamous differentiation (pure squamous cell carcinoma (SCC) or mixed urothelial carcinoma (UC/SCC)), high-grade non-keratinising squamous differentiation is difficult to identify in haematoxylin-eosin stainings. This study aims to validate routine immunohistochemical markers for squamous differentiation in a larger cohort of patients. Tissue microarrays of 89 pure SCCs and mixed UC/SCCs, 66 urothelial carcinomas (UC), precursor lesions and normal urothelium were stained for cytokeratin (CK) 5/6, CK 5/14, CK 7, CK 20 and uroplakin III. Electron microscopy was performed to confirm the differentiation. Pure SCCs displayed staining throughout the epithelium for CK 5/6 (76.6% (36/47)) and CK 5/14 (95.8% (46/48)), focal staining for CK 7 (28.9% (13/45)) and no staining for CK 20 and uroplakin III (both 0% (0/48)). UCs exhibited a basal or diffuse staining for CK 5/6 (30.2% (16/53)) and CK 5/14 (57.1% (32/56)), focal positivity for CK 7 (83.6% (46/55)), CK 20 (50.9% (29/57)) and uroplakin III (21.8% (12/55)). Each marker discriminated SCC and UC significantly (p < 0.01). A third subgroup rarely showed full epithelial staining for CK 5/6 (14.3% (1/7)) and CK 5/14 (28.6% (2/7)), focal staining for CK 7 (85.7% (6/7)) and no staining for CK 20 and uroplakin III (both 0% (0/7)). Electron microscopy could prove both, SCC and UC characteristics, revealing a transient type. A staining pattern with CK 5/6- and CK 5/14-positivity plus CK 20- and uroplakin III-negativity identified squamous differentiation in bladder tumours and revealed a third type of squamous transdifferentiation.