Patience required when evaluating radiofrequency ablation

October 15, 2008

Evaluating the efficacy of radiofrequency ablation of renal cortical tumors requires a degree of patience because histologic changes and cell death in and near lesions targeted by the treatment may continue to evolve for a year or even longer.

"Our conclusions are that it takes a certain amount of time for the radiofrequency lesions to evolve histologically," said first author Joshua M. Stern, MD, a former UT Southwestern resident working with Jeffrey Cadeddu, MD, and colleagues. "Until that time elapses, it is impossible to determine the viability of this tissue. We have determined that H&E [hematoxylin and eosin] staining at one year will determine whether there is residual disease."

There has been an ongoing dialogue as to how to follow and evaluate RF-ablated tumors ever since the introduction of the technology, said Dr. Stern, who is now a minimally invasive oncology fellow at the University of Pennsylvania's Penn Presbyterian Medical Center in Philadelphia. Much of the discussion revolves around "skip" lesions, small regions of tissue in or near the tumor that initially appear to have been unaffected by the treatment. When the technology was undergoing early evaluation, investigators would conduct a procedure, wait from 10 minutes to a month or longer, biopsy the lesion, find residual tumor cells, and inappropriately conclude that the treatment might be less than successful, he explained.

The UT Southwestern team selected 19 patients with 20 lesions who had undergone RF ablation of renal tumors. Pre-ablation biopsies of the lesions found 17 renal cell carcinomas and three oncocytomas. At 1-year follow-up, the patients exhibited no evidence of disease, such as lesion growth or enhanced areas identified by contrast computed tomography. Dr. Stern noted that the institution traditionally follows all RF ablation-treated patients with CT scans at 6 weeks, 3 months, 6 months, and 1 year. The mean follow-up at the time biopsies were taken was 26.9 months.

The patients underwent CT-guided needle biopsy of their ablated lesions, and the specimens obtained underwent H&E staining and histologic comparison with pre-ablation specimens.

Among the findings were observations that all 20 lesions were stable in size without evidence of contrast enhancement, all 20 specimens showed unequivocal cell death with no evidence of cellular viability, and histologic changes beyond 1 year demonstrated coagulative necrosis, hyalinization, immune cell infiltration, and residual ghost cells.

"While cellular architecture is preserved immediately following RFA, chronic changes demonstrate coagulative necrosis and non-viable tissue," the researchers wrote.

An earlier study concluded that intermediate-term oncologic effectiveness of the therapy appeared similar to traditional treatments for small renal masses.