Microwave ablation (MWA) is a safe and effective alternative to partial nephrectomy (PN) for the treatment of small renal masses (SRMs), with both treatment modalities associated with similar oncologic and renal function outcomes, according to study findings published recently in Urologic Oncology

“Our study confirmed that in experienced hands microwave ablation can be an effective tool in preventing local recurrence for masses less than 4 cm, with no significant difference in the change in renal function after the procedure compared to the partial nephrectomy cohorts,” said lead investigator Jennifer Mason Lobo, PhD, Associate Professor of Biomedical Informatics at the University of Virginia in Charlottesville.

Dr Lobo and colleagues analyzed retrospective data from 2009 to 2015 and prospective data since 2015 from a single-institution database. The study included 80 patients who underwent PN and 126 who had MWA. Although preoperative renal function was better in patients receiving PN and those with smaller tumors, the investigators found no significant differences in the change of renal function following the procedures.

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“Microwave ablation is the ablation modality used at the University of Virginia due in part to lower sedation requirements and shorter procedure times relative to other ablation modalities,” Dr Lobo said. “Our team wanted to compare oncological and renal function outcomes for small renal mass patients treated with microwave ablation and partial nephrectomy.”

Cumulative progression-free survival rates at 36 months were similar between the cohorts (90% for PN and 91% for MWA), the investigators reported.

Among patients with SRMs smaller than 3 cm, the PN cohort had 3 recurrences (8.3%) and the MWA cohort had 2 (3.2%). Among patients with 3-4 cm SRMs, the PN cohort had 2 recurrences (4.6%) and the MWA cohort had 6 (9.4%).

Complications developed in 35 patients: 12 (27.3%) and 8 patients (22.2%) in the PN cohort with SRMs 3-4 cm and less than 3 cm, respectively, and 7 (10.9%) and 8 (12.9%) in the MWA cohort with SRMs 3-4 cm and less than 3 cm, respectively.

Among patients with SRMs smaller than 3 cm, high-grade complications developed in 0 and 2 (3.2%) patients in the PN and MWA cohorts, respectively. Among patients with 3-4 cm SRMs, high-grade complications occurred in 4 (9.1%) and 3 (4.7%) patients in the PN and MWA cohorts, respectively.

Preoperative renal function was significantly lower in patients undergoing MWA for both tumor sizes, but there was no significant difference in the postoperative change in renal function between the cohorts for SRMs up to 4 cm.

As robotic-assisted laparoscopic PN continues to grow in popularity, PN has become the standard of care for most clinically localized tumors, the authors noted. MWA uses electromagnetic energy to achieve higher inter-tissue temperatures with larger ablation zones. RPN was performed trans-peritoneally under general anesthesia using standard clamping of the renal artery with warm ischemia time limited to 30 minutes. MWA (NeuwaveTM Ethicon) was performed percutaneously under general anesthesia using computed tomography (CT) guidance, ultrasound guidance, or a combination. Image guidance was used to place antennas and confirm position.

The median age of those treated with MWA was 67 years and it was 55 years for the PN cohort. “Our study supports microwave ablation as a safe nephron-sparing option for patients, including those that might not be surgical candidates,” Dr Lobo said. For patients who are not good surgical candidates and who are seen at centers where microwave ablation is not offered, referral to a center that regularly performs microwave ablation could offer the patient a definitive treatment for their mass, Dr Lobo said.

The median follow-up for patients with SRMs smaller than 3 cm was 35.9 months for PN and 25.6 months for MWA; the median follow-up for patients with 3-4 cm SRMs was 36.1 months and 27.3 months, respectively. The median time to recurrence for patients with SRMs smaller than 3 cm was 119.1 months for PN and 76.1 months for MWA. The median time to recurrence for patients 3-4 cm SRMs was 72.0 and 91.9 months, respectively.

The authors note that the patient cohorts were not matched for key characteristics such as age or comorbidities. The study lacked adequate statistical power to analyze relationships between tumor complexity, local recurrence, and treatment modality due to the small number of recurrences.

Jeffrey A. Cadeddu, MD, Professor of Urology and Distinguished Chair in Minimally Invasive Urologic Surgery at UT Southwestern Medical Center in Dallas, Texas, said longer follow-up of these patients is required to support MWA being an accepted ablation modality compared with cryoablation and radiofrequency ablation. “It adds to the experience with microwave energy, which is still immature relative to the 2-decade experience with cryoablation and radiofrequency ablation,” Dr Cadeddu said. “These results are encouraging, and I believe that microwave ablation will be a reasonable alternative, but not oncologically or functionally better than these other ablation technologies.”

Keith Quencer, MD, Associate Professor of Interventional Radiology at Oregon Health and Sciences University in Portland, said the study is part of a growing body of research comparing PN and ablation. “As in this study, no great difference in outcomes can be found between these two treatment modalities,” Dr Quencer said. “Patient preference and local expertise should therefore play a large role in triage of patients to interventional radiology or urology.” 

MWA is a well-established ablative modality in interventional radiology and is most often used in the liver. Use in the kidney is well described, with the most common ablative modality in current use being cryoablation. “Both of these modalities offer positives and negatives,” Dr Quencer said. “Higher bleeding risk and longer ablation time being the negative for cryoablation with the advantage being real-time visualization of the ablation zone and less deleterious effects on the collecting system. MWA, in properly selected patients, is quicker than cryoablation and with lower bleeding complications.”

Follow-up longer than 36 months is needed to determine the effect on quality of life, kidney function, recurrence, and, most importantly survival. Ideally, a 3-armed multicenter randomized controlled trial comparing active surveillance, ablation (either MWA or cryoablation), and partial nephrectomy should be undertaken, he said.


Qiu J, Ballantyne C, Lange M, et al. Comparison of microwave ablation and partial nephrectomy for T1a small renal masses. Urol Oncol. Published online August 17, 2023. doi:10.1016/j.urolonc.2023.07.008