Under‐grading of <4 cm renal masses on renal biopsy

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Abstract
Study Type – Prognosis (case series) Level of Evidence 4 What's known on the subject? and What does the study add? It is well documented that biopsy of small renal masses is inaccurate and tends to under‐estimate tumour grade compared with surgical specimens. To our knowledge there has not been a study showing grading discrepancy between biopsy and surgical excision in a large population‐based cohort. OBJECTIVE: To determine whether differences exist in tumour grade between patients who undergo partial nephrectomy (PN) and those who undergo ablation for renal tumours. PATIENTS AND METHODS: Data was obtained using the Surveillance, Epidemiology and End Results database. Patients with solitary renal tumours of P < 0.001), more likely to be married (70% vs 64%, P < 0.001), and had smaller tumours (2.4 vs 2.6 cm, P < 0.001). There were no differences in the distribution of histology between the PN and ablation groups. Tumour grade was significantly lower in tumours treated with ablation. Compared with grade 1 disease, those undergoing ablation were 30% less likely to have grade 2 ( P < 0.001), 30% less likely to have grade 3 ( P < 0.001), and 92% less likely to have grade 4 disease ( P < 0.01) than those having PN. CONCLUSIONS: There is a strong association between grade and treatment type in patients with small renal masses after controlling for baseline characteristics. As grade is determined by different methods, we think that this shows systematic under‐grading in biopsy of small renal masses.

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