BOSTON – Stereotactic radiosurgery stabilized disease or induced tumor shrinkage on imaging in most patients with inoperable localized renal cancer in a phase I trial.
There were even hints of curative potential, investigators reported at the annual meeting of the American Society for Radiation Oncology.
"We’ve certainly seen encouraging results at this point: Two of the patients at the higher doses actually had negative biopsies," Dr. Rodney J. Ellis, director of urogenital oncology at the University Hospitals Seidman Cancer Center in Cleveland, said during a press briefing.
The combined radiographic tumor response rate – stable disease or tumor regression – was 94%, but treatment was found to be incomplete or refractory among most patients who had a post-treatment biopsy. This finding suggests that higher radiation doses would be required for better tumor control, Dr. Ellis said.
Dose escalation in the trial varied from 24 Gy divided into four 6-Gy fractions to 48 Gy in four 12-Gy fractions, with dose-limiting toxicities not yet reached.
Acute toxicities were limited to grade-1 acute fatigue in two patients. Late toxicities were limited to an increase in chronic renal failure in two patients who had a baseline mean estimated glomerular filtration rate of 19.5 mL/min, corresponding to stage-4 renal disease. There were no other significant grade-3 or higher toxicities and no gastrointestinal adverse effects, he said.
The investigators looked at 20 patients, mean age 80 years, with a radiologically or biopsy-determined diagnosis of localized primary renal cancer. All were considered to be poor candidates for surgery and had no history of pelvic or abdominal radiation.
The patients were assigned to receive stereotactic radiosurgery with the CyberKnife robotic system at an initial dose of 600 cGy per fraction, followed by dose escalation of 200-cGy increments per fraction to total doses up to 48 Gy.
The dose escalation was started if the patients had not developed dose-limiting toxicity within 180 days of treatment. In all, 20 patients were enrolled: 4 at 24 Gy, 6 at 32 Gy, 4 at 40 Gy, and 6 at 48 Gy.
The institutional review board for the trial has approved enrollment of 12 additional patients at doses ranging from 48 Gy in three fractions to 60 Gy in four fractions, Dr. Ellis said.
Dr. Ellis noted that the diagnosis of primary cancer has become much more common with the advent of CT scans, which detect incidental renal masses, some of which are likely to progress. Some people suggest that incidental renal cancers should be handled with watch and wait, he noted. Also, some of these cancers may be inoperable because of patient factors.
He said that sterotactic radiosurgery "will prolong life for patients, especially if we see the kind of efficacy at the higher doses that we anticipate."
The study is supported by the National Cancer Institute. Dr. Ellis reported no relevant disclosures.