Utility of new immunohistochemical stains in urological pathology

Abstract

Background/aims A number of new immunohistochemical stains has recently become available for use in urogenital pathology. By way of illustration, we present a case of multifocal nephrogenic metaplasia of the bladder mimicking invasive urothelial carcinoma, and discuss the use of immunohistochemistry in distinguishing this entity from its malignant mimics. Case report A 76-year-old lady underwent a radical cystectomy for BCG-resistant invasive urothelial carcinoma. Although invasive high-grade urothelial carcinoma was confirmed histologically, additionally present were apparent nests of glandular cells arising subjacent to urothelial carcinoma in situ. The cells were positive for PAX8 and negative for GAT A3 and p63 immunohistochemistry, while the inverse pattern was present in the overlying urothelial carcinoma in situ. Coexistent nephrogenic metaplasia was diagnosed. Discussion As nephrogenic metaplasia can demonstrate a haphazard growth pattern, presence in the deep lamina propria or muscularis propria and occasional degenerative atypia, it can be difficult to distinguish from malignant tumours such as urothelial and prostatic carcinomas. Immunohistochemistry, including the use of recently characterised markers such as PAX8 and GAT A3, can assist in the diagnosis. Discussion is made of the utility and pitfalls of these stains in this and other situations.