Mark Klein. That leads us into clinical trials. What is the role for precision oncology in prostate cancer right now, specifically looking at particular panels? One would be the DNA repair enzyme-based genes and/or also the AR variants and any other markers.
Elizabeth Hansen. The National Comprehensive Cancer Network came out with a statement recommending germ-line and somatic-mutation testing in all patients with metastatic prostate cancer. This highlights the need to offer patients the availability of clinical trials.
Julie Graff. I agree. We occasionally get to a place in the disease where patients are feeling fine, but we don’t have anything else to offer. The studies by Robinson16 and then Matteo17 showed that (a) these DNA repair defects are present in about a quarter of patients; and (b) that PARP inhibitors can help these patients. At least it has an anticancer effect.
What’s interesting is that we have TRITON2, and TRITON3, which are sponsored by Clovis,for patients with BRCA 1/2 and ATM mutations and using the PARP-inhibitor rucaparib. Based on the data we have available, we thought a quarter of patients would have the mutation in the tumor, but they’re finding that it is more like 10% to 15%. They are screening many patients but not finding it.
I agree that clinical trials are the way to go. I am hopeful that we’ll get more treatments based on molecular markers. The approval for pembrolizumab in any tumor type with microsatellite instability is interesting, but in prostate cancer, I believe that’s about 3%. I haven’t seen anyone qualify for pembrolizumab based on that. Another plug for clinical trials: Let’s learn more and offer our patients potentially beneficial treatments earlier.
Mark Klein. The first interim analysis from the TRITON2 study found about 12% of patients had alterations in BRCA 1/2. But in those that met the RECIST criteria, they were able to have evaluable disease via that standard with about a 44% response rate so far and a 51% PSA response rate. It is promising data, but it’s only 85 patients so far. We’ll know more because the TRITON2 study is of a more pretreated population than the TRITION3 study at this point. Are there any data on precision medicine and radiation in prostate cancer?
Abhishek Solanki. In the prostate cancer setting, there are not a lot of emerging data specifically looking at using precision oncology biomarkers to help guide decisions in radiation therapy. For example, genomic classifiers, like GenomeDx Decipher (Vancouver, BC) and Myriad Genetics Prolaris (Salt Lake City, UT) are increasingly being utilized in patients with localized disease. Decipher can help predict the risk of recurrence after radical prostatectomy. The difficulty is that there are limited data that show that by using these genomic classifiers, one can improve outcomes in patients over traditional clinical characteristics.
There are 2 trials currently ongoing through NRG Oncology that are using Decipher. The GU002 is a trial for patients who had a radical prostatectomy and had a postoperative PSA that never nadired below 0.2. These patients are randomized between salvage radiation with hormone therapy with or without docetaxel. This trial is collecting Decipher results for patients enrolled in the study. The GU006 is a trial for a slightly more favorable group of patients who do nadir but still have biochemical recurrence and relatively low PSAs. This trial randomizes between radiotherapy alone and radiotherapy and 6 months of apalutamide, stratifying patients based on Decipher results, specially differentiating between patients who have a luminal vs basal subtype of prostate cancer. There are data that suggest that patients who have a luminal subtype may benefit more from the combination of radiation and hormone therapy vs patients who have basal subtype.18 However this hasn’t been validated in a prospective setting, and that’s what this trial will hopefully do.