**1. Introduction**

Bladder cancer is a frequent neoplasm [1] in which tobacco use, pollution, and other varied agents have been directly implicated in its genesis and development [2]. Most of them are composed of transitional cells of low/intermediate grade, papillary architecture, and invasion limited to the lamina propria and submucosa. However, a smaller but significant number of cases do display dismal features like high-grade, non-papillary growth patterns, and muscularis propria invasion, with these patients pursuing an aggressive clinical course.

Aside from transitional cell carcinoma (TCC), other histological subtypes, like conventional squamous cell carcinoma, adenocarcinoma, and neuroendocrine carcinoma, are quite frequently seen in clinical practice, alone or in combination, particularly in the context of high-grade cases. These cases are not the subject of this review.

Although TCC is a histologically monotonous neoplasm composed in the vast majority of cases by easily recognizable transitional cells, a small subset of cases displays a broad spectrum of architectural and/or cytological characteristics that should be recognized since some of them carry diagnostic difficulties and/or prognostic implications [3] (Table 1). This recognition is increasingly important now that very promising advances linking morphological variants with genomic signatures are being identified [4].


**Table 1.** Unusual features in bladder cancer with prognostic profiles.

Clinical practice allows the pathologist to face unusual histological subtypes of urothelial carcinomas (UC), and conventional TCC displaying focal/extensive morphologic variations of uncertain significance. This narrative collects 25 years of personal experience of the authors in the routine diagnosis of bladder cancer.
