2017 GU Cancers Symposium: Blood Test Uncovers Potential New Treatment Targets in Advanced Prostate Cancer
Analysis of free-floating cancer DNA from blood samples has yielded leads for new prostate cancer treatment targets. Using a commercially available “liquid biopsy” test in patients with advanced prostate cancer, researchers found a number of genetic changes in cell-free, circulating tumor DNA (ctDNA) in the patient’s bloodstream. The study will be presented by Sonpavde et al at the upcoming 2017 Genitourinary Cancers Symposium in Orlando, Florida (Abstract 149).
Cell-free ctDNA provides comprehensive information about all the different genetic changes in the tumor. Treatments can sometimes be tailored to the genetic changes in a tumor, but these changes evolve over time. The cell-free ctDNA tests can be used to track new genetic changes, and this information can be used to stop treatment to which resistance is emerging and to switch the patient to another treatment.
Study Details
In the study, researchers found genetic changes linked to poor outcomes, as well as changes that appear to arise as tumors become resistant to therapy. The changes in ctDNA found by the blood tests were similar to those previously reported in analyses of tumor tissue specimens, suggesting that ctDNA testing may be a viable alternative to tissue biopsy.
“This circulating tumor DNA test is now a valuable research tool to discover new molecular targets,” said lead study author Guru Sonpavde, MD, Associate Professor of Medicine at the University of Alabama. “Eventually, it may also serve as a noninvasive alternative to the traditional tumor biopsy in cases where tissue biopsy is not safe or feasible. However, we’ll need a controlled, prospective clinical trial to confirm that selecting treatment based on the molecular information from this blood test improves patient outcomes.”
The researchers analyzed cell-free ctDNA from blood samples of 514 patients with metastatic castration-resistant prostate cancer. The blood test (Guardant360), which requires only two teaspoons of patient blood, examined changes in 70 cancer-related genes. The association between DNA changes and clinical outcomes was explored in 163 patients. In addition, the researchers explored how genomic changes evolved over time in 64 patients who underwent serial blood tests.
Key Findings
Nearly all patients (94%) had at least one change detected in their ctDNA. A higher overall number of genetic changes, including changes in the androgen receptor (AR) gene, were associated with poorer treatment outcomes, such as a tendency toward shorter survival (although the difference in survival was not statistically significant).
The genes that were most often mutated included TP53 (36%); AR (22%); APC (10%); NF1 (9%); EGFR, CTNNB1, and ARID1A (6% each); and BRCA1, BRCA2, and PIK3CA (5% each). The most common genes with increased copy numbers were AR (30%), MYC (20%), and BRAF (18%). Increased cancer gene copy number can lead to overabundance of proteins that drive cancer growth. Currently, there are no approved treatments for prostate cancer that target these specific genetic mutations, although several are being tested in clinical trials.
In the group of patients who underwent periodic blood tests, new changes in AR gene were particularly common. According to the researchers, this finding suggests that developing treatments that target AR mutations may hold promise.
“As we work to tailor treatment to the molecular changes driving the growth of cancer in each patient, these blood tests appear very promising, especially for patients who are unable to undergo a tumor biopsy,” said ASCO Expert Sumanta Pal, MD, of the results.
This study was unfunded; deidentified data were provided by Guardant Health.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
