The (MC)2 risk score is a valuable tool for predicting major complications in patients undergoing renal cryoablation, according to a study published online May 7 by Radiology.

Cryoablation greatly increases the number of renal tumors that can be successfully treated percutaneously in patients, yet many complications often follow. Factors related to the tumor or patient can influence the occurrence of complications, making it more important for operators to individualize risk assessment for periprocedural complications based on patient comorbidities, tumor size and complexity.

“As the use of percutaneous cryoablation expands to include treatment of larger, more complicated renal tumors in patients with a greater number of medical comorbidities, it becomes increasingly important for interventional radiologists and urologists to understand tumor and patient-related renal cryoablation risk factors,” wrote lead author Grant D. Schmit, MD, of the Mayo Clinical School of Medicine in Rochester, Minn., and colleagues.

Although three renal tumor scoring systems exist for quantification of renal tumor complexity, they are lacking in several areas. The researchers evaluated their renal cryoablation experience to identify tumor and patient-related risk factors for major complications that follow renal cryoablation and develop a model to predict these events.

Schmit and colleagues reviewed 398 renal cryoablation procedures that were performed to identify patient and tumor-related risk factors associated with major complications. They then developed a scoring system for predicting adverse events by using risk factor weighting from a multivariate logistic regression model. The scoring system was applied to all 73 renal cryoablation procedures performed during 2012 to internally validate the model.

Of the tumor-related factors that were evaluated, Maximal tumor diameter and Central tumor location were associated with major complications. Of the patient-related factors evaluated, prior myocardial infarction and complicated diabetes mellitus were significantly associated with major complications. These findings resulted in the development of the (MC)2 risk scoring system, with a score equaling 2.5 points for tumors less than or equal to 2.5 centimeters in maximal diameter, 0.1 points for each millimeter of maximal tumor diameter for tumors greater than 2.5 centimeters, 1.5 points if it’s a central tumor location, 2.5 points if there is a patient history of myocardial infarction and 3 points is there is patient history of complicated diabetes. Based on the scoring system, the patients were divided into three groups: low-risk patients had a score of less than 5, moderate-risk had a score between 5 and 8, and high-risk had a score greater than 8.

The mean (MC)2 risk score for all renal cryoablations was 4.7. The observed major complication rates were 2 percent in the low-rise group, 12.8 percent in the moderate-risk group and 39.1 percent in the high-risk group. Application of the (MC)2 scoring system to the validation group provided a concordance index of 0.82.

“The (MC)2 score can be helpful for predicting the risk of a major cryoablation complication for a specific patient with a specific renal tumor; this information should be useful to clinicians and patients in making decisions about available renal tumor treatment options, such as surgery, ablation, or observation,” wrote Schmit and colleagues.