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


Catherine R. Harris, Department of Urology, University of California, San Francisco, 400 Parnassus Avenue A633, San Francisco, CA 94143-0738, USA. e-mail: HarrisCR@urology.ucsf.edu


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.


  • • To determine whether differences exist in tumour grade between patients who undergo partial nephrectomy (PN) and those who undergo ablation for renal tumours.


  • • Data was obtained using the Surveillance, Epidemiology and End Results database. Patients with solitary renal tumours of <4 cm treated with ablation or PN and with renal cell carcinoma (RCC) histopathology were identified.
  • • Tissue diagnosis in the ablation specimens was obtained from biopsy reports, whereas tissue from PN specimens was determined from surgical pathology.
  • • Variables analysed included: year of diagnosis, age, sex, race/ethnicity, marital status, population density, education, poverty level, and tumour size.
  • • Stacked bar graphs were created to compare the distributions of grade and histology between the groups. Multinomial logistic regression was used to determine factors independently associated with grade.


  • • In all, 7704 (87.4%) patients underwent PN and 1114 (12.6%) underwent either radiofrequency ablation or cryoablation.
  • • The PN patients were younger at diagnosis (59 vs 68 years, 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.


  • • 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.