Cryoablation improves survival more than thermal ablation for renal cell carcinoma patients

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Cryoablation may be associated with longer overall survival than heat-based thermal ablation in clinical T1a renal cell carcinoma (RCC), concludes a recent study published in the Journal of Vascular Interventional Radiology. To date, this is the largest study comparing overall survival between two ablative therapies in these patients.

“Further research with the use of randomised controlled trials or retrospective studies, with more details on technologies, local outcomes, and complications, is required to identify patients best suited to treatment with either approach”, the authors recommend.

Jing Wu (Second Xiangya Hospital, Central South University, Changsha, China) et al note that a clinical trial comparing the effectiveness of cryoablation with thermal ablation is “not likely to be developed or completed”, and thus set out to assess the survival outcomes of these two treatment modalities using the US’ National Cancer Database (NCDB). Established in 1989, this is a clinical oncology database of hospital registry data gathered from more than 1,500 Commission on Cancer-accredited facilities and sponsored by the American College of Surgeons and the American Cancer Society. Over 70% of newly diagnosed cancer cases in the USA are captured by NCDB data.

A total of 6,258 patients who received either cryoablation (3,936 patients) or heat-based thermal ablation (2,322 patients) between 2004 and 2014 were included in the study.

The three-, five-, and ten-year survival rates were, respectively, 91%, 82%, and 62% for cryoablation and 89%, 81%, 55% for heat-based thermal ablation. Wu and colleagues report that patients treated with cryoablation had more comorbidities that those treated with thermal ablation. They say that this finding “supports previous studies suggesting heat-based thermal ablation as [sic] less effective in managing larger masses”.

Detailing their results, the authors write: “On univariate Cox regression analysis, compared with cryoablation, the hazard of mortality was increased for patients treated with heat-based thermal ablation (p=0.031). On multivariate Cox regression analyses adjusted for age, facility type, facility location, insurance status, education level, income, residence, Charlson-Deyo score, tumour size, and treatment, cryoablation remained associated with longer overall survival compared with heat-based thermal ablation (p=0.021).”

This observed difference in overall survival was only apparent in tumours larger than 2cm, according to the study investigators. The authors say that “This is in accordance with a previous retrospective study of 445 patients that demonstrated similar outcomes between cryoablation and heat-based thermal ablation when treating masses ≤3cm”.

Centre and experience were not found to have an effect on overall survival. “In fact”, the authors write, “patients who went to facilities reporting ≥100 cases over the past 10 years had shorter survival than those who went to facilities reporting <100 cases”. They posit that this difference in survival is due to the fact that patients were sicker in the more experienced centres, as large academic centres take complex cases where patients are more likely to have increased comorbidities. Another explanation the authors suggest is that “with high-volume centres reporting more heat-based thermal ablations than cryoablations, the shorter survival may be related to the shorter survival associated with the procedure itself”.

The study authors describe ablation as “a nephron-sparing minimally invasive approach that is typically used for patients who are not optimal surgical candidates or who have masses within a solitary functioning kidney or in association with renal dysfunction”. They explain that, although partial nephrectomy “remains the most common treatment for clinical T1a RCC, ablative therapies serve as a less invasive alternative and offer distinct advantages in both complications rate and cost-effectiveness”.

Wu and colleagues acknowledge several limitations of their study. Being retrospective, they say that the potential for selection bias “must be considered”. Secondly, the study only reports on overall survival, and not cancer-specific survival, “which would be expected to have more direct implications on treatment consideration”, the authors write. They also list the inability to distinguish approach and ablation type (radiofrequency ablation or microwave ablation) in the NCDB dataset, the potential for underreporting of cases performed by interventional radiologists, the inability to assess impact on patients’ quality of life, and any potential unknown confounders outside of those accounted for in the study as limitations.

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