Accuracy of on-bench biopsies in the evaluation of the histological subtype, grade, and necrosis of renal tumours.

AIMS: Few data are available on the diagnostic accuracy of kidney tumour biopsy. METHODS: We sought to evaluate morphological diagnostic accuracy--such as histotype, Fuhrman grading, and necrosis--on a series of renal biopsies and matched whole tumours. RESULTS: Among 56 renal tumours, the benign instances consisted of six oncocytomas (10.7%), one angiomyolipoma (AML; 1.8%), and one metanephric adenoma (1.8%). Malignant tumours consisted of clear cell renal cell carcinoma (RCC) in 37 cases (66.1%), papillary RCC in six cases (10.7%), chromophobe RCC in three cases (5.4%), and unclassified RCC in one case (1.8%). Core biopsies were conclusive in 53 cases (94.6%), identifying six (10.7%) benign and 47 (83.9%) RCCs. The accuracy in identifying histological subtype was 92%, and the concordance between core biopsies and surgical specimens was nearly perfect (κ = 0.858; p < 0.001). With regard to nuclear grade, the concordance index was only moderate (κ = 0.253) and the concordance between core biopsies and surgical specimens was fair (κ = 0.20; p = 0.11), such as for necrosis. CONCLUSIONS: We concluded that the accuracy in identifying histological subtype is high. Tumours with oncocytic features are the most problematic for diagnosis. Results for nuclear grades and coagulative tumour necrosis are less convincing.