Post-RP radiation: Test could guide selection, timing

The muddy waters of patient selection and timing of post-prostatectomy radiation therapy may be clearer. Find out how.

The muddy waters of patient selection and timing of post-prostatectomy radiation therapy may be clearer with the use of a genomic test for prostate cancer, recent study results suggest.

“The optimal timing of post-prostatectomy radiation therapy is a subject of debate. Common practice is to wait for PSA rise after surgery before intervening with radiation treatment. The results of this study suggest that we can use a genomic test to identify a group of men who will benefit from earlier administration of additional local treatment,” explained lead author Robert Den, MD, of the Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia in a press release.

Researchers from Thomas Jefferson University and the Mayo Clinic, Rochester, MN published findings from their positive validation study of the Decipher Prostate Cancer Classifier (GenomeDx Biosciences) online in the Journal of Clinical Oncology (Feb. 9, 2015).

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The study included 188 prostate cancer patients who received radiation therapy after radical prostatectomy at Thomas Jefferson University and Mayo Clinic between 1990 and 2009.

The authors found that patients with low genomic risk (as determined by Decipher) may be optimally managed with observation after radical prostatectomy, while those with high genomic risk may be better managed earlier with adjuvant radiotherapy.

The Decipher test validated as the top risk factor for metastasis with 83% accuracy for predicting metastasis and stratifying patients with low, average, and high genomic risk with 0%, 9%, and 29% 5-year cumulative incidence of metastasis (p=.002).

The results also indicated that Decipher may predict benefit from radiation therapy: Patients with average-to-high Decipher risk who were treated with adjuvant radiation therapy had a 5-year metastasis incidence of only 6% compared to 23% (p=.008) for those who waited for PSA recurrence to trigger initiation of salvage therapy. Overall, patients with higher Decipher results who received adjuvant radiation had an 80% reduction in risk of metastasis compared to those who received salvage radiation (HR: 0.20 [95% CI], p<.04).

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In addition, the study found no disadvantage for salvage therapy in men with low-risk Decipher results, suggesting that these men may improve quality of life by waiting for possible PSA rise rather than taking a course of immediate radiation therapy after radical prostatectomy.

In an email to Urology Times, co-author Leonard G. Gomella, MD, emphasized the study’s significance to care decisions in this setting.

“The use of adjuvant and salvage radiotherapy following radical prostatectomy has been controversial. While several supporting trials have been completed and a joint paper by ASTRO and the AUA has endorsed the use in selected patients, the exact criterion for who should receive and when to administer postoperative radiation remains unclear. Using genomics, this is the first study to be predictive for treatment outcomes in the postoperative setting and has the potential to change our standard of care,” said Dr. Gomella, also of Thomas Jefferson University.

Mayo Clinic has a financial interest in the Decipher test. Dr. Den has received research funding from GenomeDx Biosciences and has been compensated by the company for travel-related expenses. Dr. Gomella is a consultant/adviser to Astellas Pharma, Janssen Pharmaceuticals, and Algeta/Bayer, and has received research funding from Astellas, Janssen, and Myriad Genetics. Three study co-authors are employees of GenomeDx Biosciences, and four serve as consultants/advisers to the company.

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