A renal mass in the setting of a nonrenal malignancy : When is a renal tumor biopsy appropriate?

Frequently, a renal mass is identified when patients with cancer undergo studies for staging or surveillance. In determining whether it represents a metastasis, patients are frequently subjected to percutaneous renal biopsies. The authors evaluated their experience with this dilemma to formulate management guidelines. The authors reviewed the medical records of 100 consecutive patients with nonrenal malignancies diagnosed with renal masses at presentation or follow-up. Renal mass histology was available for all patients after nephrectomy or biopsy. Clinical characteristics were assessed to identify factors predictive for a renal metastasis versus a primary renal neoplasm. The only factors predictive of a metastasis to the kidney were progression of the nonrenal malignancy and lack of enhancement of the renal mass (P < 0.0001). Forty-six patients (46%) had evidence of progression of their nonrenal malignancy in addition to the renal mass. In these patients, the probability of a metastasis to the kidney was 86% (95% confidence interval [CI], 57.2-98.2%) without renal mass enhancement and 32% (95% CI, 14-55%) with enhancing renal masses. None of the 54 patients without signs of progression of their nonrenal malignancy proved to have metastases to the kidney, regardless of the imaging characteristics of the mass (zero probability; 95% CI, 0-7%; P < 0.001). In patients presenting with renal masses and another clinically localized malignancy, renal mass biopsies were not indicated, as the mass rarely represented a metastasis. These patients may opt for close surveillance or extirpation based on the prognosis of their nonrenal malignancy.