Histologic grading of urothelial carcinoma: a reappraisal.

A uniform grading system for bladder cancer will allow for valid comparison of treatment results among different centers. The introduction of the World Health Organization (2004)/International Society of Urological Pathology classification is a welcome step toward standardization of treatment and follow-up regimens. The greatest source of controversy with the World Health Organization (2004)/International Society of Urological Pathology classification system centers on the diagnosis of papillary urothelial neoplasm of low malignant potential. Some feel that papillary urothelial neoplasm of low malignant potential terminology increases the complexity of histologic grading and does not accurately reflect biologic potential. Papillary urothelial neoplasm of low malignant potential is a low-grade papillary urothelial neoplasm with a substantial incidence of recurrence and progression. In the distinction of papillary urothelial neoplasm of low malignant potential from noninvasive low-grade papillary urothelial carcinoma, there is considerable interobserver variability. For these reasons, some investigators believe that papillary urothelial neoplasm of low malignant potential is, in essence, an entity that was previously designated grade 1 urothelial carcinoma in the World Health Organization 1973 grading system. In addition, treatment and follow-up regimens for patients with papillary urothelial neoplasm of low malignant potential do not typically differ from those prescribed for low-grade, noninvasive urothelial carcinoma, further minimizing the clinical need for the papillary urothelial neoplasm of low malignant potential distinction to be made. We propose abandonment of the terminology "papillary urothelial neoplasm of low malignant potential" in bladder tumor classification. Full-genome searches for prognostic and predictive molecular gene expression signatures as cancer markers have shown significant promise. Recent advances in the molecular grading of these tumors may eventually supplant traditional morphologic grading systems, allowing a more precise and objective assessment of the tumors' biologic potentials.