Updates and controversies in contemporary grading of clear cell renal cell carcinoma and papillary renal cell carcinoma.

A decade into the formal adoption of the World Health Organization (WHO)/International Society of Urological Pathology (ISUP) grading system for clear cell renal cell carcinoma (CCRCC) and papillary renal cell carcinoma (PRCC), newer grading concepts, innovative approaches and some issues have emerged. A comprehensive review of the literature on the WHO/ISUP grading system and other grading approaches for CCRCC and PRCC was conducted. Updates and issues are presented on the following: (1) validation studies on WHO/ISUP grading; (2) grade elements including heterogeneity, grades 1 versus 2, types of multinucleated tumour cells, 'grade spectrum' of spindle cells, impact of sarcomatoid change in grade 4 RCC, percent (%) high grade, % sarcomatoid change and rhabdoid change versus sarcomatoid change; (3) grade applications including observer agreement, needle biopsy grade accuracy (correlation with nephrectomy grade) and grading of multifocal RCCs; (4) grade in papillary tumours including heterogeneity and on small (≤1.5 cm) neoplasms; and (5) novel grading or risk categories including incorporation of necrosis into grading and pattern or architectural-based grading. Practice guidance for some of the issues is provided when feasible or where data are sufficient. This review highlights the recent updates and controversies in the use of WHO/ISUP grading and on novel approaches to grading for CCRCC and PRCC. This review may serve as a best practice guide in addressing some of the grading issues and will help identify gaps in our understanding and use of grading for CCRCC and PRCC that can inform future research.