The new World Health Organization/International Society of Urological Pathology (WHO/ISUP) classification for TA, T1 bladder tumors: is it an improvement?

The World Health Organization/International Society of Urological Pathology (WHO/ISUP) consensus classification of urothelial neoplasms of the urinary bladder was developed in an attempt to both improve upon prior classification systems as well as to adopt a classification system that would have widespread acceptance. Prior to this classification system, numerous diverse grading schemes for bladder cancer existed whereby the same lesion seen by different pathologists would result in very different diagnoses solely based on definitional differences of lesions. Another strength of the consensus classification system is that it provides detailed histological criteria for papillary urothelial lesions. In contrast, prior grading systems for bladder tumors were vague and subjective. The current classification system allows for designation of a lesion (papillary urothelial neoplasm of low malignant potential), which biologically has a very low risk of progression, yet is not entirely benign. In the past, these lesions were a source of controversy, as some experts in the field required very restrictive criteria for the diagnosis of papilloma and would label such lesions as malignant. Other experts in the field, not wanting to label a patient with such a low-grade papillary lesion as having carcinoma, would diagnose these lesions as papilloma. This intermediate category allows both schools of thought to diagnose a lesion as not fully malignant, yet still documents need for additional follow-up. Since its inception, several studies have been published documenting the relationship of tumors classified using the WHO/ISUP system to prognosis. These articles are summarized within this review.