Biopsy of small renal mass may help avoid unnecessary treatment

Badar M. Mian, MD

The incidental finding of small renal masses (≤4 cm) has increased significantly over the past several decades in parallel with the increased use of cross-sectional imaging. Depending on the tumor size, 15% to 25% of small masses may be benign, and an equal number may be low grade. To avoid unnecessary treatment, percutaneous biopsy of the small renal mass has increased for the past several years, but its use remains highly variable.

Sinks et al report that a kidney tumor program with mandated small renal mass biopsy can alter treatment decisions and potentially prevent unnecessary interventions.¹ The investigators evaluated the management of small renal masses over time in the group that underwent discretionary renal mass biopsy compared with the group where renal mass biopsy was mandated prior to ablation of the mass.

The investigators’ Kidney Tumor Program database of small renal masses spanned from 2000 to 2020. In April 2017, the clinical pathway began to mandate renal mass biopsy prior to all ablation procedures. All biopsies were core-needle biopsies obtained under ultrasound or CT guidance, and cryoablation was the only modality used for ablating these small renal masses. The postmandate biopsy cohort included 167 patients, whereas the control group (prior to mandated biopsy) included 1035 patients. Most patients were men, with a median age of 64 years and median tumor size of 2.1 cm.

The investigators reported a significant increase in the overall biopsy rate from 7.6% to 19%. Although the biopsy mandate was targeted at the group undergoing tumor ablation, the increase in the biopsy rate for small renal masses was observed across all treatment groups, including those undergoing surgery or active surveillance. Interestingly, the rates of ablation following biopsy did not change significantly; the investigators observed a significant change in surgical intervention and active surveillance. The rate of active surveillance increased from 15% to 43%, and the rate of surgical intervention decreased from 46% to 22%. Patients with a positive biopsy result, compared with patients with benign (nonmalignant) results, were to undergo surgery (32% vs 23%) or an ablation procedure (31% vs 23%). In contrast, patients with a negative biopsy result were more likely to undergo active surveillance than those with a positive biopsy result (15% vs 8.5%).

Knowledge of the biopsy results seems to influence management options. In this cohort, renal mass biopsy was associated with a reduction in active treatment and increased use of active surveillance of small renal masses. The biopsy rate increased for most subgroups of patients except for those in the lowest quartile of socioeconomic status who, consequently, were not afforded the opportunity to avoid potentially unnecessary treatment. Whether this is due to poor adherence by the patient (due to access or income) or provider-related factors (eg, implicit bias) is an opportunity for further study.

Interestingly, the biopsy mandate did not significantly change the rate of ablation before or after the biopsy mandate (10.9% vs 8.9%). This may be related to the workflow of the biopsy and ablation procedure. Nearly half of patients did not have biopsy pathology information available at the time of ablation. It is not clear why an ablation was performed without knowing the pathology results, because the reason for the mandated biopsy was to identify nonmalignant tumors.

Confidence in the renal mass biopsy procedure depends on local expertise, including interventional radiology and pathology. We routinely perform biopsy for all small renal masses because of a low rate of complications and low rate of nondiagnostic yield (>8%), whereas other centers report nondiagnostic biopsy rates of 10% to 20%. Findings from this study demonstrate an association between biopsy results and treatment decision. Patients who are found to have a positive biopsy result overwhelmingly proceed to surgery or ablation (83%), and patients with a negative biopsy result are significantly more likely to avoid aggressive treatment in favor of active surveillance. Contemporary renal mass biopsy is generally a safe and effective procedure. Along with repeat imaging, it should be used with increasing regularity to avoid unnecessary management of small or low-grade renal masses.

Reference

1. Sinks A, Miller C, Holck H, et al. Renal mass biopsy mandate is associated with change in treatment decisions. J Urol. 2023;210(1):72-78. doi:10.1097/JU.0000000000003429