Introduction:

While current AUA guidelines recommend using renal mass biopsy when it “may influence management,” it is possible that biopsy is currently underutilized, leading to higher than necessary rates of intervention for benign disease. To optimize how biopsy is used, we aimed to identify groups of patients where routine biopsy (i.e., a strategy of obtaining biopsy in all patients with certain types of masses) may be useful in (1) identifying benign disease, and (2) avoiding potentially unnecessary surgery. We evaluated the association between tumor complexity, type of surgery performed, and rates of benign pathology within the MUSIC collaborative to inform our understanding of which mass types may optimally benefit from routine biopsy.

Methods:

MUSIC is a quality improvement collaborative that identifies patients with newly diagnosed renal masses prospectively. We queried the MUSIC database for patients undergoing partial or radical nephrectomy from 2017-2024 with an available RENAL nephrometry score. Using Fisher’s exact test, we compared (1) rates of benign final pathology stratified by nephrometry score groups (low: 4-6, intermediate: 7-9, high: 10-12), and whether a renal mass biopsy was performed and (2) rates of benign radical nephrectomy for intermediate and high RENAL scores between masses that were biopsied versus not biopsied preoperatively.

Results:

Of 943 cases, RENAL scores were low in 19%, intermediate in 57%, and high in 24%. Biopsy rates were 23% in low, 21% in intermediate, and 27% in high RENAL score masses. Low RENAL score masses rarely had radical nephrectomy (13%), none of which were benign. Intermediate RENAL score masses had radical nephrectomy in 38% of cases; the rate of benign radical nephrectomy for intermediate score cases undergoing biopsy was 0/51 (0%) versus 19/151 (13%) for those not undergoing biopsy. High RENAL score masses had radical nephrectomy in 76% of cases; the rate of benign radical nephrectomy for high score cases undergoing biopsy was 1/45 (2%) versus 10/129 (8%) for similar masses without biopsy. For intermediate and high RENAL scores, biopsy was associated with a ten-fold reduction in risk of benign radical nephrectomy relative to no biopsy (1/96 [1%] vs. 29/280 [10%], p = 0.002; 95% CI=[1.4, 72.0]).

Conclusion:

In a large real-world cohort, roughly 10% of radical nephrectomies for intermediate-high complexity masses have benign final pathology. Routine renal mass biopsy of intermediate and high complexity renal masses could significantly reduce the rate of radical nephrectomy for benign masses. Renal mass biopsy may be overused for low complexity renal masses that are amenable to partial nephrectomy. Overall, in a large real-world sample, renal mass biopsy is not currently optimally used. Prospective validation of these findings, ideally in a randomized trial, could help define an optimal biopsy strategy and inform updates to the AUA renal mass guidelines. With these data, renal mass biopsy can be targeted to appropriate patients and masses, to inform surgical planning and minimize unnecessary procedures.

Funding: Blue Cross Blue Shield of Michigan