ORLANDO, FL—Five years after treatment with stereotactic body radiotherapy, nearly all patients (97%) with early-stage prostate cancer treated in a poster study have had no biochemical relapse (Abstract 9).
In that study, led by Patrick Kupelian, MD, Vice Chair of Radiation Oncology at UCLA Jonsson Comprehensive Cancer Center, 99 percent of patients with Gleason Grade 6 or lower prostate cancer were free of recurrence as measured by prostate-specific antigen (PSA) five years after undergoing radiation treatment. About 92 percent of men who had a Gleason score of 7 were also free of relapse after five years. The difference in outcomes between those with a Gleason score of 6 or less and those with a Gleason 7 score was not statistically significant, Kupelian said.
“In a relatively large cohort of localized prostate cancer patients treated with stereotactic body radiotherapy with a long follow-up period, excellent efficacy was demonstrated, with 97 percent of patients being free from any relapse.”
Overall, biochemical relapse, which was defined as a rise greater than 2 ng/mL above the PSA nadir, was observed in four of the 135 patient outcomes analyzed over the five-year follow-up. “Although further follow-up is necessary to establish longer-term efficacy the results at the five-year mark are encouraging for low- and intermediate-risk cases,” Kupelian said, adding that even if the efficacy for the technique overall is equivalent to that for standard fractionated radiation therapy, there are still benefits in terms of convenience and cost.
In the study, 99 percent of the patients with low-risk prostate cancer had achieved biochemical relapse-free status at five years, vs. 93 percent for the intermediate- and high-risk patients, but that difference was not statistically significant.
The study involved reviewing data on the outcomes of 1,101 patients treated at eight institutions between 2003 and 2011, focusing on a subset of 135 cases involving men for whom five years of follow-up data were available. In all the cases, the men were diagnosed with clinical Stage T1 of T2A prostate cancer. About 80 percent of the patients were diagnosed with a Gleason score of 6 or less; the rest had a score of 7.
At the start of treatment, the median PSA pretreatment level was 5.1 ng/mL; 77 percent of patients fell into a low-risk group; 22 percent, intermediate risk; and two percent of the patients were judged to be at high risk for relapse.
The median radiation dose was 36.25 Gy, delivered either with four or five fractions. Most of the treatment failures occurred in patients who were below the median in radiation dose—specifically, those who received 35 Gy—about 42 percent of the patient population. About 47 percent of the men received 36.25 Gy, and 11 percent received 38 Gy or higher.
The researchers observed a trend for worse outcomes if patients received total radiation doses of 35 Gy, but this was not confirmed on multivariate analysis. “These results compare favorably with other modalities with similar follow-up periods,” the team noted.
A total of 21 percent of the men treated with radiation also received androgen-deprivation therapy, but the outcomes between the groups were not statistically different: “Multivariate analysis showed only Gleason score to be an independent predictor of biochemical relapse. Pretreatment and radiation dose were not,” the researchers said.
‘Highly Enriched with Low-Risk Patients’
Asked to comment on the study for this article, Ian Thompson, MD, Professor and Chair of Urology at the University of Texas Health Science Center at San Antonio, said: “This is a fairly contemporary cohort followed for a fairly short period of time that is highly enriched with low-risk patients. It is not surprising that you would have this survival data with active surveillance in this type of population.”
Thompson, who delivered a keynote address to the symposium, also observed that 80 percent of the patients had Gleason scores of six or less: “At many institutions across the United States, it would be an unusual patient with that score who would be actively treated. These results are basically the same that we would see with active surveillance.”
The pendulum of treatment for low-risk patients has been swinging more to the side of surveillance, rather than definitive therapy, he said. “With the active surveillance and more testing and screening that is being done today, a Gleason 6 tumor found today is generally smaller, is found earlier, and has a better prognosis than a Gleason 6 tumor found 10 years ago.
“In the absence of a randomized comparative group, I am hard-pressed to make conclusions other than what I usually tell my patients: If you have a Gleason 6 tumor or a low-volume Gleason 7 tumor, regardless of what you do, your outcome is likely to be pretty good.”