Diagnosis of small renal masses (SRM): Biopsy before treatment
Author: Assoc. Prof. Anders Kjellman
The use of biopsies to diagnose small renal masses (SRM, ≤4 cm) before treatment remains significantly underutilised. Kidney tumours, alongside testicular tumours, are among the few solid tumours routinely operated on without a confi rmed cancer diagnosis. This practice results in unnecessary surgeries for benign kidney lesions, exposing patients to avoidable risks and increasing healthcare costs without clinical benefit. Such inefficiencies in resource utilisation underscore the need for a paradigm shift in the urological management of kidney tumours.
The European Association of Urology (EAU) guidelines on kidney cancer note that only a small proportion of kidney lesions are biopsied prior to surgery. Consequently, approximately 20–30% of surgically removed SRMs are found to be benign. However, the guidelines recommend biopsy only in specific scenarios, such as when the patient is a candidate for active surveillance, ablation, or in cases of metastatic disease. Of course, patients who are unsuitable for active treatment due to frailty should not undergo biopsy.
It is well-documented that a significant proportion of small kidney lesions are benign. For lesions up to 4 cm (cT1a), approximately 30% are benign, with oncocytomas and fat-poor angiomyolipomas being the most common types. In Sweden, a review of T1a kidney cancer cases revealed that only about 20% of patients underwent biopsy before surgery. This figure is consistent across many European countries, meaning that between 20% and 33% of patients with T1a tumours undergo unnecessary surgery.
The value of biopsies
Renal mass biopsies have demonstrated excellent sensitivity and specifi city. A large meta-analysis found these metrics to be signifi cantly higher than for nearly all other solid tumours, including prostate and breast cancers. Moreover, biopsy results show a high degree of concordance with final pathological diagnoses and provide valuable insights for further tumour risk classification.
Although imaging methods such as sestamibi scans and girentuximab PET-CT have improved predictive capabilities in recent years, their sensitivity and specificity remain lower than those of biopsies, making biopsies an essential diagnostic tool. Addressing the barriers to biopsy Why, then, are biopsies not more frequently performed before initiating treatment? Discussions with colleagues reveal three primary concerns:
1. Biopsies are risky
2. Results are unreliable and will not alter treatment decisions
3. They prolong the diagnostic process and increase costs
Let us examine these objections.
- Biopsies are risky: The complication rate for kidney mass biopsies is exceptionally low. Fewer than 1% of patients experience bleeding, and such cases typically resolve without intervention. This complication rate is lower than that for most other solid tumours. Concerns about tumour seeding along the biopsy tract are largely anecdotal. A meta-analysis of over 5,000 patients calculated the risk of seeding to be just 0.0019% when biopsies are performed using co-axial techniques.
- Results are unreliable: As noted, renal mass biopsies demonstrate high sensitivity and specificity, making them reliable forclinical decision-making. Studies show that implementing renal mass biopsy can reduce the rate of surgeries for benign lesions to as low as 3%. For initial inconclusive biopsies – seen in 10–15% of cases – a second biopsy can decrease this rate to below 3%.
- Increased costs: Integrating biopsies into the diagnostic process does not cause significant delays or compromise patient outcomes. On the contrary, a systematic approach to biopsies reduces costs by preventing unnecessary surgeries for benign lesions. Preliminary data from a health economic analysis conducted by the Kidney Cancer Treatment Group in Sweden estimated that increasing biopsy rates for T1a tumours from 25% to 75% would save millions of Swedish kronor annually. For T1b tumours, the costs were cost-neutral but provided clinical benefits.
Implications of increased biopsy usage
- Follow-up requirements: Biopsy diagnoses may result in more patients requiring active surveillance.
- Diagnostic challenges: Oncocytomas can be challenging to diagnose accurately, leading to lower diagnostic concordance and increased need for follow-up. Nonetheless, real-world evidence suggests that higher biopsy rates reduce surgical interventions and promote active surveillance, benefiting both patients and healthcare systems.
Conclusion
It is time to prioritise patient safety and efficiency by adopting biopsies as a standard diagnostic tool for SRM. By trusting the evidence, we can reduce unnecessary surgeries and usher in a new paradigm where treatment decisions for SRM are informed by biopsy results.
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Assoc. Prof. Anders Kjellman presents on hot topics in renal cell carcinoma management on Sunday, 23 March 15:15 – 16:45.