Percutaneous biopsy of renal cell carcinoma underestimates nuclear grade.

Objectives: To assess the accuracy of renal biopsy for predicting the final nuclear grade and histologic subtype. Small renal masses can be safely observed in select patients who are poor surgical candidates. Renal biopsy may help identify patients who are candidates for observation.

Methods: A total of 81 patients (29 female, 52 male) underwent percutaneous biopsy of their renal mass with ultrasound or computed tomography guidance. Percutaneous 18-gauge biopsy cores were obtained, and all patients subsequently underwent radical nephrectomy or partial nephrectomy. Preoperative biopsy results were compared with postoperative specimens.

Results: The mean tumor size was 5.3 cm (range, 1-17). Overall, biopsy correctly identified 71 of 81 (88%) histologic subtypes. The preoperative biopsy correctly identified 62 of 64 (97%) clear cell renal carcinomas, 9 of 10 (90%) papillary carcinomas, 0 of 3 (0%) chromophobe carcinomas, and 1 of 2 (50%) oncocytomas. The final pathologies for 2 nondiagnostic biopsies were clear cell renal carcinoma and inflammatory pseudotumor. For 67 tumors, the pathologists assigned a nuclear grade for both the biopsy and the final specimen. The biopsy correctly identified 29 of 67 (43%) final nuclear grades. The biopsy underestimated the nuclear grade in 37 of 67 (55%) cases. In 7 of 67 (10%) cases, the biopsy nuclear grade increased by 2 when compared with the final grade. The biopsy rarely overestimated the nuclear grade; 1 case (1%) that was assigned a grade 2 on biopsy was assigned a grade 1 after nephrectomy.

Conclusions: Core biopsies for renal masses underestimate nuclear grade in most cases; however, histologic subtype is more reliably assessed, particularly for clear cell renal tumors.