Objective

The AUA guidelines recommend renal mass biopsy (RMB) for renal masses suspected to be hematologic, metastatic, inflammatory, or infectious, as well as whenever obtaining histologic information may influence the management strategy for a solid mass; RMB is not required for young or healthy patients who are unwilling to accept uncertain findings or for older, frail patients who will be managed conservatively independent of RMB findings.^1,2 Whether to perform RMB in the workup of new, clinical stage T1 renal masses (RMs) is, therefore, largely a decision made by the individual patient and urologist. In this study, we explore the chosen management strategies for patients based on whether they underwent an RMB for cT1RM. Through this analysis, we assessed the utility and impact of RMB on clinical decision-making for treating cT1aRMs (≤4 cm) and cT1bRMs (4.1-7.0 cm).

Methods

Patient data were collected from the prospectively maintained MUSIC-KIDNEY (Michigan Urological Surgery Improvement Collaborative-Kidney mass: Identifying and Defining Necessary Evaluation and therapY) registry, with methods for data collection being previously outlined.³ Data collected for the purposes of this study include age, sex, race, tumor type identified on radiographic imaging (solid, complex cyst, or indeterminate), tumor size (cT1a or cT1b), and preoperative estimated glomerular filtration rate. Biopsy pathology was also gathered (benign, favor benign, indeterminate, favor malignancy, malignant) in addition to histotype (oncocytoma, angiomyolipoma, other benign, clear cell renal cell carcinoma (RCC), papillary RCC, chromophobe RCC, or other cancer). Final surgical pathology was collected and reported in the same categories as the biopsy pathology.

Results

Of 3,466 cT1RM patients evaluated between 2017 and 2022, 18% underwent RMB (see Table). There were significant differences in tumor size and type, with median size of 2.6 cm vs 3.0 cm in the no RMB and RMB groups, respectively. Patients with cystic tumors were unlikely to undergo RMB (9 of 271, 3.3%) and they were, therefore, excluded from subsequent analyses. For patients with solid or indeterminate cT1aRMs, 58% of those without RMB were managed by active surveillance (AS), 36% had a nephron-sparing intervention (NSI), which includes partial nephrectomy, tumor ablation, and stereotactic body radiotherapy, and 6% had a radical nephrectomy (RN). For cT1aRM patients with an RMB, 44% elected AS, 48% had NSI, and 8% had RN (see part A of Figure). There was a net decrease of 14% in the use of AS, and a concomitant increase in intervention, for cT1aRMs. Conversely, for patients with a cT1bRMs and no RMB, 23% pursued AS, 33% had NSI, and 44% had RN. For cT1bRM patients with RMB, 33% elected AS, 37% had NSI, and 30% had RN (see part B of Figure). In cT1bRM, there was a net increase of 10% in AS, a 4% increase in partial nephrectomy, and a 13% decrease in RN.

Table. Patient Demographics and Clinical Characteristics

Discussion

One clear benefit of obtaining an RMB in patients with cT1RMs prior to treatment is making histologic information about the mass available to inform the treatment decision. Our findings demonstrate that the subsets of patients undergoing RMB for cT1a and cT1bRMs may receive more appropriate management. Patients who undergo RN have a significantly increased risk of developing chronic kidney disease relative to AS and NSI.⁴ Given the increased renal functional loss from RN, and morbidity from RN and NSI, a decision for AS that does not compromise oncologic outcomes is of benefit to the patient. When patients with benign renal masses (and selected patients with cancers of low malignant potential) avoid intervention due to RMB, it is a win-win-win for the patient, provider, and health care system.

Prior studies have shown that obtaining an RMB increases the use of AS in the management of cT1RM.^5,6 Surprisingly, we found that in patients with cT1aRMs, AS was used less frequently in patients undergoing RMB than in those without RMB. This finding could be due to selection biases, as patients who undergo RMB may not be similar to those who forgo RMB. But it could also be the case that patients who undergo RMB may not select AS as readily after a cancer diagnosis is made. Current guidelines support the use of AS in selected patients with cT1aRM, as the clinical course of these masses is often indolent throughout the timeline of AS.^1,2,7 Our data suggest that not all patients with cT1aRM are ideal candidates for RMB, specifically those who already have chosen AS over immediate intervention.

On the other hand, RMB may be ideal for the majority of patients with a cT1bRM. In patients who underwent RMB, there was greater utilization of both AS and NSI and a significant decrease in RN (P = .0027) when compared to patients who did not have RMB (see part B of Figure). In this group of patients, our data showed that for every 8 biopsies obtained, 1 kidney would be saved from RN. While there may be selection biases at play in the subgroup of cT1bRM patients who underwent RMB as well, the potential for benefit here seems greater as most patients will be recommended to undergo intervention at initial evaluation.

Conclusions

The proportion of patients selecting various treatments for cT1RM is not the same for the groups of patients undergoing or forgoing RMB. Our findings are novel in 2 regards. First, we found that more patients with cT1aRM underwent immediate intervention after RMB than those not having RMB. Second, RMB appears to impact treatment choice more for cT1b than cT1a masses. For patients with cT1bRM, 1 kidney was spared from RN by every 8 RMBs performed. We recommend that RMB be recommended for all patients with cT1bRM, and for patients with cT1aRM in whom intervention is being considered.