Dysplasia and carcinoma in situ of the urinary bladder.

Urothelial dysplasia (low-grade intraurothelial neoplasia) is recognized as a premalignant urothelial lesion in the 2004 World Health Organization (WHO) classification system. Although clarification of the diagnostic criteria of urothelial dysplasia has improved in recent years, there is still a lack of interobserver reproducibility. Active clinical follow-up is mandatory in patients with a diagnosis of urothelial dysplasia since it constitutes a marker of urothelial instability, and disease progression, in up to 19% of cases. The differential diagnosis of urothelial dysplasia is with other flat urothelial lesions with atypia, including flat urothelial hyperplasia, reactive urothelial atypia, urothelial atypia of unknown significance, and urothelial carcinoma in situ (high-grade intraurothelial neoplasia). In most cases, especially when small amounts of tissue are available, morphologic features alone may not be sufficient for diagnosis. Immunohistochemistry can be of help in selected cases, and a panel of cytokeratin 20, p53, and CD44 may help in the diagnosis. The use of HER2, p16, and Racemase remains as an option pending validation. Herein, we present the pathologic features and clinical significance of urothelial dysplasia and carcinoma in situ with emphasis on differential diagnosis from common flat lesions with atypia.