The cytologic diagnosis of low-grade transitional cell carcinoma.

Current theory suggests that transitional cell carcinoma (TCC) occurs as either of 2 disease processes, each of which has a distinct cytologic appearance and clinical course: low-grade and high-grade TCC. Urinary cytology has become a mainstay technique for monitoring disease recurrence in patients with TCC. Most cases of high-grade TCC can be diagnosed accurately in urinary cytology specimens. However, the cytologic diagnosis of low-grade TCC is difficult; these tumors exhibit subtle cytomorphologic alterations that are difficult to distinguish from benign or reactive processes. The cytologic criteria most useful for diagnosing low-grade TCC in urinary cytology specimens are reviewed. Additionally, the discussion includes some of the new ancillary tests that are emerging as possible diagnostic aids for the detection of low-grade urothelial neoplasms.