Pathological diagnosis is the foundation of effective cancer treatment. It not only helps avoid unnecessary treatment for benign tumors but also supports the development of individualized therapeutic strategies. When small renal masses (SRMs) are detected, some clinicians opt for biopsy, while others express concerns about its risks, reliability, and cost-effectiveness.At the European Association of Urology (EAU) Annual Meeting held from March 21 to 24, 2025, Professor Anders Kjellman of Karolinska Institute, Sweden, presented a compelling case for the value of pre-treatment biopsy in managing SRMs. UroStream summarizes his key perspectives for readers seeking to stay at the forefront of urologic oncology practice.Current Clinical Landscape: Biopsy Remains Underused in Small Renal Masses
Despite advancements in imaging and surgical techniques, biopsy remains underutilized in the diagnosis of small renal masses (SRMs, ≤4 cm). Notably, kidney tumors—along with testicular cancer—are among the few solid tumors not routinely confirmed histologically prior to surgery. This can lead to unnecessary surgical interventions for benign renal lesions, exposing patients to avoidable risks and increased healthcare costs without added clinical benefit. As such, revisiting and updating the management approach to renal tumors is of considerable clinical significance.
According to the European Association of Urology (EAU) Renal Cancer Guidelines, only a minority of renal masses currently undergo biopsy before surgery. Postoperative pathology reveals that approximately 20% to 30% of SRMs are actually benign. The guidelines recommend performing biopsy only under specific circumstances, such as when patients are undergoing active surveillance, ablation therapy, or when metastatic disease is present. Naturally, biopsy should be avoided in patients whose frail health status makes them unsuitable for definitive treatment.
There is substantial evidence indicating that a significant proportion of SRMs are benign. For example, approximately 30% of lesions ≤4 cm (cT1a) are non-malignant, with the most common subtypes being oncocytomas and angiomyolipomas. In Sweden, a retrospective review of T1a renal cancer cases showed that only about 20% of patients received a biopsy prior to surgery. This aligns with trends across many European countries and implies that 20% to 33% of patients with cT1a tumors may be undergoing unnecessary operations.
The Case for Biopsy: High Sensitivity, Specificity, and Diagnostic Confidence
Renal mass biopsy demonstrates high sensitivity and specificity—superior to that of biopsies for most other solid tumors, including prostate and breast cancers. A large meta-analysis confirmed that biopsy results closely align with final pathology and offer critical data for tumor risk stratification.
Although modern imaging technologies, such as 99mTc-sestamibi (MIBI) scans and girentuximab PET-CT, have improved diagnostic accuracy, their sensitivity and specificity still fall short when compared to biopsy. Therefore, biopsy remains an essential diagnostic tool for accurate characterization of small renal masses.
Barriers to Biopsy: Why Is It Still Underused?
Given its diagnostic value, why isn’t biopsy used more frequently before initiating treatment for small renal masses? Among European urologists, three main concerns are often cited:
- Biopsy poses risks
- Biopsy results are perceived as unreliable and unlikely to influence treatment decisions
- Biopsy may delay diagnosis and increase costs
Let’s address these concerns individually:
First, regarding the perceived risk, the complication rate for renal mass biopsy is extremely low. Fewer than 1% of patients experience bleeding, and in most cases, this resolves without intervention. This rate is lower than that observed in biopsies of most other solid tumors. Fears about tumor seeding along the biopsy tract are largely overstated. A meta-analysis involving more than 5,000 patients found that when using coaxial needle technique, the risk of tumor seeding was just 0.0019%.
Second, renal mass biopsy has high sensitivity and specificity, making it a reliable tool for guiding clinical decisions. Studies show that biopsy can reduce surgery for benign tumors to as low as 3%. For initially inconclusive biopsies—seen in roughly 10–15% of cases—a repeat biopsy can lower this uncertainty rate to below 3%.
Lastly, incorporating biopsy into the diagnostic workflow does not significantly delay treatment or compromise outcomes. In fact, a structured biopsy approach can help avoid unnecessary surgeries for benign lesions and thus reduce overall healthcare costs. Preliminary data from the Swedish Kidney Cancer Group’s health economics analysis suggest that increasing the biopsy rate for T1a tumors from 25% to 75% could save millions in healthcare spending annually. For T1b tumors, although the cost-effectiveness is less pronounced, the clinical benefits remain compelling.
The Broader Impact of Increased Biopsy Use
A rise in biopsy utilization could lead to more patients entering active surveillance pathways. While accurate diagnosis of oncocytomas remains challenging—leading to lower diagnostic concordance and greater follow-up requirements—real-world data supports the notion that higher biopsy rates reduce unnecessary surgical intervention and promote conservative management. This benefits both patients and healthcare systems alike.
Conclusion: Time for a Shift—Biopsy as Standard in SRM Diagnosis
The time is ripe to establish biopsy as a standard diagnostic tool for small renal masses. This approach prioritizes patient safety and diagnostic efficiency. Guided by robust evidence from evidence-based medicine, we can reduce avoidable surgical interventions and embrace a new paradigm in SRM management—where treatment decisions are increasingly informed by biopsy results.
Professor Anders Kjellman
- Professor, Department of Clinical Science, Intervention and Technology, Karolinska Institute (2024–2027)
- Lecturer, Department of Urology and Renal Medicine, Karolinska Institute (2023)
