A genetic test, called Decipher Prostate RP, can help to identify those prostate cancer patients with a relapse after surgery who will benefit most by adding androgen deprivation therapy (ADT) to radiation therapy, a new analysis of clinical trial data shows.
“Identifying which patients with recurrent disease are most likely to benefit from hormonal therapy will improve our ability to extend patient survival, while minimizing unnecessary toxicity for a large group of men with prostate cancer,” Felix Feng, MD, vice chair of radiation oncology at University of California, in San Francisco, said in a press release.
The data, “Transcriptome profiling of NRG Oncology/RTOG 9601: Validation of a prognostic genomic classifier in salvage radiotherapy prostate cancer patients from a prospective randomized trial,” were presented at the 2020 American Society of Clinical Ongology (ASCO) Genitourinary Cancer Symposium, held Feb. 13–15, in San Francisco.
Until recent years, men whose prostate cancer returned after a prostatectomy (surgical removal of the prostate) were usually treated with radiation therapy alone. Often, the disease continued to progress with metastasis in nearly half of them.
The RTOG 9601 Phase 3 clinical trial (NCT00002874), conducted from 1998 to 2003, changed standard of care for these patients. It found that adding ADT, a hormone therapy, to radiation treatment significantly reduced the likelihood of metastasis and extended the patients’ lives compared to radiation only.
The trial involved 760 patients, who were randomly assigned to either seven weeks of radiation therapy plus two years of bicalutamide (an ADT), or radiation therapy plus a placebo.
But a recent exploratory analysis of RTOG 9601’s data revealed that the combination therapy was only beneficial to men with higher levels of prostate cancer antigen (PSA) — a marker of prostate cancer progression — at the time of disease relapse.
Notably, men with lower PSA levels (less than 1.5 ng/ml) not only were seeing no benefits from the combination treatment but were also at a higher risk of death from causes other than cancer.
The Decipher Prostate RP by Decipher Biosciences — a genetic test widely used to predict a prostate cancer patient’s risk of metastasis within five years — was found to accurately identify those men who would benefit most from adding ADT to radiation therapy, independently of PSA levels.
This test provides a Decipher score predicting a patient’s metastasis risk based on 22 disease biomarkers. So far, it was used to help determine if a patient had a higher risk of metastasis and should be considered for radiation therapy after surgery.
In the new study, researchers evaluated whether Decipher Prostate RP could also predict those patients most likely to benefit from adding ADT to radiation therapy upon disease relapse.
To do this, the scientists determined the Decipher score of the tumors of 352 men who participated in the RTOG 9601 study, and looked for associations between their Decipher scores and treatment benefits. These men were representative of the overall group of patients, and had a median follow-up of 13 years.
Results found that men with a high-risk Decipher score showed significantly greater benefits from the combination therapy than did those with a low-risk Decipher score. Benefits included a lower likelihood of metastasis, and of prostate cancer-related and overall mortality.
These predictions were independent of standard risk-associated clinical and disease-associated parameters, including age, race, cancer stage, and PSA levels at the beginning of the study.
Notably, the data also supported the combination therapy’s lack of benefit in men with lower levels of PSA (less than 0.7 ng/mL).
The study validated in a clinical context Decipher Prostate RP as the most accurate predictor of metastasis, and prostate cancer-specific and overall survival in these patients.
It could help to determine a patient’s absolute benefit from adding ADT to radiation therapy after surgery, and improve treatment decisions.
“Decipher Prostate RP improves upon clinical and [disease-associated] risk stratification methods and informs the use of hormonal therapy, making it a reasonable and recommended component of the prostate cancer standard of care,” Feng said.
Data from nine other studies involving Decipher tests also were presented at the symposium.
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