The study retrospectively reviewed every patient who underwent ablation of a biopsy-proven T1 renal cell carcinoma at the center between March 2013 and June 2023. In total, 50 ablation procedures were performed on 46 tumors in 45 patients, with a mean tumor diameter of just 2.6 centimeters. The patients were not a healthy bunch: the mean age was 70 years, ranging from 45 to 85, and the average Charlson Comorbidity Index score was 5.5, a figure that corresponds to an estimated ten-year survival of only about 21 percent. In other words, these were precisely the patients for whom major surgery carries prohibitive risk, and yet their cancer outcomes matched or exceeded those reported in surgical series.

The technical machinery behind the results is worth unpacking. Radiofrequency ablation, the workhorse of the series, uses an internally cooled 17-gauge cluster electrode perfused with chilled saline at 70 milliliters per minute, tipped with a 2.5-centimeter active segment. The device runs a 12-minute impedance-controlled program, delivering alternating current that causes ionic agitation and resistive heating in the surrounding tissue, cooking tumor cells to destruction. The number of probe placements was scaled to tumor size, and the goal was a circumferential 0.5-centimeter margin of treated tissue around the tumor, a buffer designed to catch any microscopic extension beyond the visible mass.

Microwave ablation, introduced at the center in 2018, works differently. A 14-gauge antenna emits electromagnetic waves at 2450 megahertz, causing water molecules throughout the field to oscillate and generate frictional heat directly, rather than relying on conduction from the probe. That allows higher temperatures, larger ablation zones, and shorter treatment times, with power settings of 40, 60 or 100 watts and exposure times of 5, 10 or 15 minutes adapted to the tumor dimensions measured on pre-procedural CT. Cryotherapy, used in only a single case here, employs a 14-gauge cryoprobe and two freeze-thaw cycles to kill cells through ice-crystal formation, with the advantage of real-time monitoring of the ice ball during the procedure. Notably, if a tumor sat within 1.5 centimeters of the ureter, the team chose cryoablation, since thermal energy near the collecting system risks injuring this delicate structure.

Almost all procedures, 49 of 50, were performed under general anesthesia with combined CT and ultrasound targeting by one of three fellowship-trained interventional radiologists with five to eight years of ablation experience. Technical success, meaning satisfactory completion of the planned treatment protocol, was achieved in 100 percent of cases. Primary efficacy, defined as complete eradication of the tumor on the first follow-up CT or MRI, was 94 percent: 43 of 46 tumors. Median hospital stay was a single day, and follow-up imaging with multiphasic CT or contrast-enhanced MRI was performed at 3, 6, 9 and 12 months and then annually.

The survival statistics are the headline numbers. Overall survival was 97.4 percent at one year and 88.5 percent at both three and five years. Local tumor progression-free survival stood at 100 percent at one year and 95.2 percent at three and five years. Most strikingly, cancer-specific survival at five years was 100 percent: not a single patient in the cohort died of kidney cancer. The three deaths recorded during follow-up, from COVID-19 pneumonitis, cerebrovascular accident and decompensated liver disease at 4, 29 and 31 months respectively, were all unrelated to the malignancy. Kidney function was also preserved, with no statistically significant change in serum creatinine between the pre-procedure and one-month post-procedure measurements, a critical point given that many of these patients had limited renal reserve to begin with.

Complications occurred after 8 percent of procedures, four of 50, and all four followed radiofrequency ablation. One patient developed a pneumothorax during the procedure requiring chest drain insertion; another suffered a hemothorax, also managed with a chest drain, which prolonged the hospital stay to 13 days. A third developed a perinephric collection three months after ablation, causing mild hydronephrosis that was treated with image-guided drainage and antibiotics. The fourth experienced acute urinary retention, likely related to general anesthesia, resolved with a catheter that was successfully removed 48 hours later. That complication profile compares favorably with the published literature: a systematic review covering 2,258 thermal ablations reported an overall complication rate of 16 percent and a major complication rate of 3 percent.

Perhaps the most provocative finding is the head-to-head comparison between the two heat-based modalities. Radiofrequency ablation achieved primary efficacy in 100 percent of its 28 tumors, while microwave ablation succeeded in only 82 percent of its 17, a statistically significant difference. The failure pattern was telling: tumors in which microwave ablation failed were significantly larger, with a median diameter of 3.8 centimeters versus 2.4 centimeters for those successfully treated. Only three of the 17 microwave patients failed primary treatment, so the numbers are small, but the result aligns with a well-established inverse relationship between tumor size and ablation success. Other groups have reached similar conclusions, with one study reporting that increasing tumor size more than doubled the hazard of primary efficacy failure, and another finding residual tumor rates of 5.6 percent for T1a tumors versus 19.1 percent for larger T1b lesions.

The authors, however, urge caution in interpreting the radiofrequency-versus-microwave gap. Microwave ablation was adopted at the center only in 2018, and the technology arrived with a steep learning curve. Manufacturers marketed microwave systems as less susceptible to the heat-sink effect, in which flowing blood near large vessels carries heat away from the ablation zone, and as capable of treating larger tumors faster with a single antenna. But at the time of introduction, there were no in-vivo treatment charts for the kidney; radiologists had to plan therapy using ablation measurements made on ex-vivo animal liver. Compounding the problem, the microwave antenna produces a non-spherical ablation zone that behaves differently from radiofrequency and cryotherapy probes: the distal treatment margin sits proximal to the antenna tip, whereas with radiofrequency and cryoablation the zone extends beyond the electrode tip. Misjudging that geometry, even slightly, can leave residual viable tumor at the margin, and two of the three failures in this series involved endophytic tumors abutting the collecting system, an anatomically demanding location.

The broader context matters too. Guidelines from the European Association of Urology and the American Urological Association still recommend partial nephrectomy as first-line treatment for T1 renal cell carcinoma, citing a lack of high-level evidence for ablation. But every comparison between ablation and surgery is confounded by selection bias: surgical series enroll younger, healthier patients, while ablation is disproportionately offered to the elderly and comorbid. A large retrospective comparison of 1,057 partial nephrectomies against 180 radiofrequency and 187 cryoablation cases found the surgical patients were significantly younger and healthier. Against that backdrop, the Dublin results, 100 percent technical success, 94 percent primary efficacy, 95 percent five-year local control and zero cancer deaths in a cohort averaging age 70 with heavy comorbidity, are difficult to dismiss. The study has the usual limitations of a small, single-center, retrospective design, and only six patients were followed to five years. Still, as imaging picks up ever more small, asymptomatic kidney tumors on incidental CT scans, the case for a needle-based treatment that sends patients home the next day, with their kidneys and their cancer prognosis intact, is becoming steadily harder to ignore.

Subject of Research: Image-guided thermal ablation outcomes for T1 renal cell carcinoma over ten years

Article Title: Image guided energy-based ablation of T1 renal cell cancer: a ten-year single centre experience

Article References: Ryan, J. P. C., Lynch, O. E., McGuire, B. B., & Cantwell, C. P. (2025). Image guided energy-based ablation of T1 renal cell cancer: a ten-year single centre experience. CVIR Oncology, 1(1), Article 2. https://doi.org/10.1007/s44343-025-00001-7

Image Credits: AI Generated

DOI: 10.1007/s44343-025-00001-7

Keywords: renal cell carcinoma, tumor ablation, radiofrequency ablation, microwave ablation, cryotherapy, interventional radiology, kidney cancer, T1 tumors, overall survival, cancer-specific survival, nephron-sparing therapy, CT-guided procedures