Clear cell renal cell carcinoma: validation of World Health Organization/International Society of Urological Pathology grading

Aims In 2012, the International Society of Urological Pathology ( ISUP ) introduced a novel grading system for clear cell renal cell carcinoma (cc RCC ) and papillary renal cell carcinoma. This system is incorporated into the latest World Health Organization renal tumour classification, being designated WHO / ISUP grading. This study was undertaken to compare WHO / ISUP and Fuhrman grading and to validate WHO / ISUP grading as a prognostic parameter in a series of clear cell RCC . Methods and results Analysis of 681 cases of cc RCC showed that 144 tumours could not be assigned a Fuhrman grade on the basis of ambiguous grading features. The application of WHO / ISUP grading resulted in a general down‐grading of cases when compared with Fuhrman grading. In a sub‐group of 374 cases, for which outcome data were available, 9.3% were WHO / ISUP grade 1, 50.3% were grade 2, 24.1% grade 3 and 16.3% grade 4, while the distribution of Fuhrman grades was 0.4% grade 1, 48.7% grade 2, 29.4% grade 3 and 21.5% grade 4. There were no recurrence/metastases amongst patients with WHO / ISUP grade 1 tumours and there was a significant difference in outcome for WHO / ISUP grades 2, 3 and 4. For Fuhrman grading the cancer‐free survival was not significantly different for grade 2 and grade 3 tumours. On multivariate analysis WHO / ISUP grade and pT staging category were found to retain prognostic significance. Conclusions The study demonstrates that FG cannot be applied in >20% of cases of cc RCC and the WHO / ISUP provides superior prognostic information.