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Microwave Ablation: Another Nephron-sparing Option for Localized RCC

Key findings

  • In a retrospective study of 38 patients with stage T1 renal cell carcinoma, there were no major intraprocedural complications or morbidities
  • The five minor complications were small, perinephric hematomas that were managed conservatively
  • The technical success rate was 100%
  • Microwave ablation achieved nephron preservation similar to what has been previously reported with radiofrequency ablation and cryoablation

Localized renal cell carcinoma (RCC) is frequently treated with image-guided tumor ablation, a minimally invasive option. Radiofrequency ablation and cryoablation are the two most frequently used ablation technologies and have been shown to preserve renal function, even in patients with preexisting chronic kidney disease (CKD) and multifocal disease.

For the newest method, microwave ablation, results showing early oncologic efficacy are encouraging, but the effect on renal function is still unclear. The most recent data from a two-year retrospective study at Massachusetts General Hospital published in the Journal of Vascular and Interventional Radiology shows that microwave ablation preserves renal function in patients with localized stage T1 RCC.

Ronald S. Arellano, MD, co-director the Center for Image-Guided Cancer Therapy, and Interventional Radiologist Raul N. Uppot, MD, at Massachusetts General Hospital, and colleagues reviewed the records of 38 adults who underwent percutaneous microwave ablation, guided by computed tomography (CT), between October 2015 and December 2017. There were 28 men and 10 women with an average age of 69 years (range, 51–88 years).

Collectively, the patients had 44 stage T1N0M0 RCCs. The median tumor size was 2.5 cm. Most tumors, 28, were clear-cell type, while 13 were papillary type and three were unclassified.

There were no major intraprocedural complications or morbidities, the researchers report. The five minor complications (13%) were small, asymptomatic perinephric hematomas that did not require blood transfusion or other care. These occurred early in the researcher's experience with microwave ablation.

Technical success, defined as an ablation zone entirely encapsulating the targeted lesion on CT, was achieved for all tumors.

One month after ablation, imaging showed that 42 tumors (95%) had achieved complete response, with partial response in the other two. Both of them were treated with repeated microwave ablation and achieved a complete response.

The researchers evaluated three measures of renal function:

  • Estimated glomerular filtration rate (eGFR)
  • Creatinine level
  • Blood urea nitrogen level

There was no significant change in any of these measures from before ablation to one month afterward.

Even more importantly, these measures remained unchanged throughout follow-up (median length, 16 months; range, 6–27 months). The absolute change in eGFR following microwave ablation was nearly equivalent to the changes seen in published case series of radiofrequency ablation and cryoablation.

There were no statistically significant changes in the distribution of patients among CKD stages at one month, one year and last follow-up. Similarly, the rates of new-onset decline in eGFR were not statistically significant following ablation.

The researchers comment that all ablations in this study were performed with a single antenna to help minimize the risk of bleeding complications. Theoretically, they warn, clustered radiofrequency ablation electrodes and multiple cryoprobes increase the bleeding risk based simply on the number of punctures of the renal capsule.

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