Ketamine cystitis as a mimic of carcinoma <i>in situ</i>

Aims: To describe the histopathological features of a series of patients with ketamine‐related cystitis. Methods and results: Seventeen patients with ketamine‐related cystitis, who had undergone biopsy, were identified and reviewed. Twelve showed ulceration with significant urothelial atypia. In 10 of these, immunohistochemistry was performed; 9/10 had high p53 immunoreactivity and 7/10 had moderate to high levels of Ki67 reactivity, but all were negative for cytokeratin 20. Conclusions: Ketamine can lead to reactive urothelial changes that can mimic carcinoma in situ , but the long‐term cancer risk remains unknown.