Urothelial tumors with villous morphology: Histomorphology and role of immunohistochemistry in diagnosis.

Villous adenoma and urothelial carcinoma with villoglandular differentiation (UCVGD) are rare urothelial tumours showing villous morphology, the former being a preneoplastic entity and the latter being a malignant one. The detailed immunohistochemistry of these entities is previously not described in the literature. Moreover, a limited biopsy sample of UCVGD or a villous adenoma with or without adenocarcinoma may be difficult to distinguish on the basis of the histomorphology alone. An immunohistochemical panel comprising of GATA3, p63, β-catenin, CK7 and CK20 was performed on five cases of UCVGD and three cases of villous adenoma with the aim of studying the expression of the proteins thereby aiding in the diagnosis of these entities in a limited surgical pathology specimen. The mean age of UCVGD was 66.8 years and all the patients were male. All the cases of UCVGD were associated with high grade papillary urothelial carcinoma with lamina propria invasion. The immunohistochemical panel showed strong nuclear GATA3 expression in the urothelial component of UCVGD. Interestingly, the high grade and the low grade villoglandular components of UCVGD also expressed GATA3 (nuclear) with a progressive loss of expression from the high grade to the low grade component. The villous adenomas showed negativity or aberrant cytoplasmic positivity for GATA3. The β-catenin showed a gradual loss of membranous expression from villous adenoma to low grade and high grade villoglandular components of UCVGD with a patchy membranous expression in the urothelial component of the UCVGD. p63 showed strong nuclear positivity in the urothelial component and uniform negativity in the villous adenoma and villoglandular component of UCVGD irrespective of its grade, thereby distinguishing the villoglandular component from the urothelial component. The urothelial component of UCVGD showed strong membranous CK7 expression and was higher than the CK20 expression in the urothelial component. In contrast, CK20 expression was higher in villous adenoma as compared to CK7. There was no difference in the expression of CK7 and CK20 in the villoglandular components and low grade and high grade villoglandular areas. The above-mentioned immunohistochemical pattern may help to distinguish the UCVGD from the villous adenoma.