[Nested variant urothelial carcinoma: diagnostic difficulties].

Nested variant urothelial carcinoma is a recently identified variant of urothelial carcinoma which is difficult to diagnose due to its resemblance to other benign bladder lesions, such as hyperplasia of Von Brünn nests. The authors present three clinical cases of this variant of urothelial carcinoma and emphasize the importance of clinical, cytological, histological and immunohistochemical criteria for the diagnosis and the need for early and adapted therapeutic management, as this type of bladder tumour, wrongly considered to be benign up until the early 1990s, is just as invasive as high-grade urothelial carcinoma.