San Antonio, October 20, 2015— For men with prostate cancer who have had a prostatectomy and salvage radiation therapy (SRT), analyzing their tumor genome provides clues as to whether their cancer will metastasize, therefore enabling clinicians to better personalize treatment options, according to research presented today at the American Society for Radiation Oncology's (ASTRO's) 57th Annual Meeting.

Prostate cancer treatment varies based on the severity and stage of the disease, with some patients requiring prostatectomy, which is the surgical removal of the prostate. For those patients who develop elevated prostate-specific antigen (PSA) levels following a prostatectomy, indicating that cancer cells remain in the body, additional treatment with SRT is generally the next step in treatment. Depending on other clinical indicators, the cancer metastasizing may be of concern and patients might also receive, in addition to RT, aggressive hormone therapy, which can aid in treating the cancer by suppressing male hormones.

The recurrence of a high PSA level alone is not an ideal indicator of future metastatic disease; therefore, researchers in this study looked to determine if a genomic classifier (GC), known as a validated predictor of metastasis, could distinguish the patients for whom additional, aggressive therapy is beneficial from those for whom SRT on its own is likely sufficient.
The study evaluated 166 prostate cancer patients, 53 African-American men (32 percent) and 113 Caucasian-American men (68 percent) who received SRT between 1990 and 2010 at Thomas Jefferson University, Veteran Affairs Medical Center Durham, and Mayo Clinic. GC scores were calculated for each patient based on genomic analysis of their own tumor tissue. A post-surgical sample was used from each patient's removed prostate (a tissue sample was removed from the prostatectomy specimen from the area containing the highest Gleason score) and compared to the patient's Cancer of the Prostate Risk Assessment Postsurgical (CAPRA-S) scores using survival c-index, competing-risks and Cox regression analysis for the prediction of metastasis. A patient's CAPRA-S scores are based on clinical risk factors such as pre-surgical PSA score; Gleason score (a grading system used to help evaluate the prognosis of men with prostate cancer using samples from a prostate biopsy); area around the prostate affected by cancer; and lymph node involvement.

Data indicated that a patient's GC score was the most significant factor in predicting the development of metastases five years after salvage radiation therapy, with GC low-risk patients having a 2.8 percent incidence of metastases at five years, GC average-risk patients having 5.8 percent incidence and GC high-risk patients having 33.5 percent as compared to 17 percent, 2.3 percent and 15 percent incidence of metastases in patients with low, average and high CAPRA-S scores, respectively. For those patients who were determined to be at low-risk by GC, there was no difference in the incidence of metastases regardless of the PSA value at which salvage radiation was initiated. For men with high risk, there was a significantly higher incidence of metastases in men receiving salvage radiation therapy with a PSA greater than 1 ng/ml as compared to those with PSA between 0.2-1 ng/ml.

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