Nested variant of transitional cell carcinoma with osseous metaplasia of the urinary bladder: a case report and review of published reports.

Nested variant of transitional cell carcinoma (NV-TCC) of the bladder is a rare and relatively new entity. The tumor is aggressive contrasted by its benign histopathologic appearance, and characterized by irregular urothelial nests and/or tubules. Herewith, a case with exceptional osseous metaplasia is presented emphasizing its diagnostic difficulties, because it can be confused with benign diseases or conventional TCC.