[The WHO/ISUP grading system for renal carcinoma]

Area of Science:

• Oncology
• Pathology
• Urology

Background:

• Histological tumor grading is crucial for renal cell carcinoma (RCC) prognosis.
• The International Society of Urologic Pathologists (ISUP) introduced a novel grading system in 2012, focusing on nucleoli characteristics.
• This system was validated for clear cell and papillary RCC subtypes.

Purpose of the Study:

• To introduce the World Health Organization (WHO)/ISUP grading system for renal cell carcinoma.
• To detail the criteria for each grade within the new system.
• To highlight the international adoption and validation status of the WHO/ISUP grading system.

Main Methods:

• The ISUP grading system categorizes RCC into four grades (1-4) based on nucleoli visibility and eosinophilia at specific magnifications (×400 and ×100).
• Grade 4 includes tumors with extreme pleomorphism or rhabdoid/sarcomatoid morphology.
• The system's validation was performed for clear cell and papillary RCC, with a recommendation against grading chromophobe RCC using this system.

Main Results:

• The ISUP grading system, focusing on nucleoli, provides a standardized method for assessing RCC.
• The system has been validated for clear cell and papillary RCC, demonstrating prognostic value.
• The World Health Organization (WHO) recommended the ISUP grading system at a consensus conference, leading to its international implementation.

Conclusions:

• The WHO/ISUP grading system is now the international standard for prognostic assessment of specific renal cell carcinoma subtypes.
• While validated for clear cell and papillary RCC, its prognostic utility for other subtypes requires further investigation.
• The system can be used descriptively for RCC subtypes not formally graded by this system.