Cryoablation for kidney tumor patients shows promise

Mar 30 2007

Mayo Clinic researchers report that freezing kidney tumors through percutaneous cryoablation shows promise for patients who are not good candidates for surgery.

Their early findings showing short-term success in more than 90 percent of selected patients are published in this month's issue of Radiology.

The standard treatment for kidney tumors is surgery, providing a high likelihood of a long-term cure. For some patients, surgery is not an option, and Mayo's urologists and radiologists collaborated to find alternatives for these individuals. If these patients are frail due to age or illness or are not able to have surgery because of other factors, percutaneous cryoablation may be an option.

"This procedure appears to be a good option for some patients," says Thomas Atwell, M.D., Mayo Clinic radiologist and the study's primary investigator. "It makes their hospital stay and recovery time very short and surgical stress is minimal." He cautions that this procedure is not ideal for everyone, noting that it is an option for only a relatively small subset of patients.

Percutaneous ablation uses needles to penetrate the skin and deliver directly to the tumor either high-intensity, tissue-destroying heat through radiofrequency ablation, or freezing cold through cryoablation. Mayo Clinic's radiologists are among the most experienced in the world in performing ablation techniques, and have treated nearly 300 kidney tumors either with radiofrequency ablation or cryoablation. Radiofrequency ablation (RFA) burns away the tumor, while cryoablation freezes it.

Mayo Clinic doctors had previous experience with liver tumor cryoablation when they added kidney tumor cryoablation in 2003. Today's report contains the largest published results for percutaneous cryoablation patients. Mayo researchers report that not only can this technique be an alternative to surgery, but that in some cases, it has benefits over RFA.

Previous experience in percutaneous RFA led the researchers to recognize that it has two important limitations. Tumors larger than 3 centimeters are difficult to treat with RFA, with increased rates of technical failures and tumor recurrence. Also, the area being treated cannot be effectively monitored with computed tomography (CT) or ultrasound. The Mayo study findings show that cryoablation can be used for some larger tumors with simultaneous operation of multiple cryoprobes guided by ultrasound. The ablation margin (the edge of the frozen tissue) can be accurately monitored with CT, to ensure that the total tumor mass is treated.

The researchers reviewed the records of the 23 men and 17 women with kidney cancer treated with percutaneous cryoablation at Mayo Clinic between March 12, 2003, and Aug. 4, 2005. They found that this treatment was chosen over RFA for reasons such as larger tumor size, proximity of tumor to ureter or bowel, or a central location on the kidney. Cryoablation was successful in 38 of the 40 patients, with no repeat treatment necessary.

In percutaneous cryoablation, one or more hollow needles are inserted through the skin directly into a tumor. Doctors can observe and guide the insertion by combined use of ultrasound and CT. The needle, or cryoprobe, is filled with argon gas, which results in rapid freezing of the tissue to temperatures of -100? C; and the tissue is then thawed by replacing the argon with helium. The procedure consists of two freezing and thawing cycles, seeking a frozen margin of approximately 5 millimeters beyond the tumor edge to ensure death of the entire tumor. After the cryoprobes are removed, small bandages are placed over the skin puncture sites, and the patient spends one night in the hospital before returning home.

Surgeons continue to seek less invasive methods than the traditional radical nephrectomy (removal of cancerous kidney) for the treatment of small tumors, and percutaneous cryoablation is now on the list. With the incidence of kidney cancer steadily increasing over the last 20 years, and the American Cancer Society predicting nearly 52,000 people will be diagnosed this year, with nearly 13,000 dying from it, another option for some patients is good news say the researchers.

"Additional study is still necessary, but we are confident that percutaneous cryoablation will continue to be a good option for some of our patients," says Bradley Leibovich, M.D., study co-author and Mayo Clinic urologist. "We've seen good results in the initial follow-up with these patients, and hope that the long-term results prove this to be a safe alternative for some kidney tumors." While the researchers caution that they need five to 10 years of follow-up to be able to consider this a curative treatment, they are optimistic about future findings.