International Society of Urological Pathology Expert Opinion on Grading of Urothelial Carcinoma

Context Grading is the mainstay for treatment decisions for patients with non–muscle-invasive bladder cancer (NMIBC). Objective To determine the requirements for an optimal grading system for NMIBC via expert opinion. Evidence acquisition A multidisciplinary working group established by the International Society of Urological Pathology reviewed available clinical, histopathological, and molecular evidence for an optimal grading system for bladder cancer. Evidence synthesis Bladder cancer grading is a continuum and five different grading systems based on historical grounds could be envisaged. Splitting of the World Health Organization (WHO) 2004 low-grade class for NMIBC lacks diagnostic reproducibility and molecular-genetic support, while showing little difference in progression rate. Subdividing the clinically heterogeneous WHO 2004 high-grade class for NMIBC into intermediate and high risk categories using the WHO 1973 grading is supported by both clinical and molecular-genetic findings. Grading criteria for the WHO 1973 scheme were detailed on the basis of literature findings and expert opinion. Conclusions Splitting of the WHO 2004 high-grade category into WHO 1973 grade 2 and 3 subsets is recommended. Provision of more detailed histological criteria for the WHO 1973 grading might facilitate the general acceptance of a hybrid four-tiered grading system or—as a preferred option—a more reproducible three-tiered system distinguishing low-, intermediate (high)-, and high-grade NMIBC. Patient summary Improvement of the current systems for grading bladder cancer may result in better informed treatment decisions for patients with bladder cancer.