A recent study found that measuring circulating tumor cells (CTCs) is a reliable way to predict later treatment response and survival prospects in men when metastatic prostate cancer is first diagnosed. The test may help providers to decide which patients should receive standard treatment vs who might stand to benefit from new drug trials. The research, part of a phase III clinical trial funded in part by the National Cancer Institute (NCI) of the National Institutes of Health, was published by Goldkorn et al in JAMA Network Open.
“No one, until now, has looked at whether CTC counts can be used right at the beginning, when a man first presents with metastatic prostate cancer, to tell us whether he’s going to live a long or short time, or whether or not he will progress with therapies,” said Amir Goldkorn, MD, lead author of the study and Associate Director of Translational Sciences at the USC Norris Comprehensive Cancer Center at the Keck School of Medicine in Los Angeles.
The research leveraged a U.S. Food and Drug Administration–cleared liquid biopsy technology (CellSearch) at the Norris Comprehensive Cancer Center to detect and measure CTCs in blood samples. Patients with more CTCs had shorter median survival lengths and a greater risk of death during the study period. Those with more CTCs also had shorter progression-free survival.
The researchers say the blood test may help to quickly identify patients who are unlikely to respond to standard treatment options. Those men may benefit from a more intensive approach to therapy, including clinical trials of new drugs that may have more side effects but could improve survival in these high-risk patients.
Counting CTCs
The research was part of a phase III clinical trial of the NCI-funded SWOG Cancer Research Network. Baseline blood samples from 503 patients with metastatic prostate cancer, who were participating in a new drug trial, were sent to the Keck School of Medicine team for analysis.
To analyze the blood samples, the test uses immunomagnetic beads, antibodies attached to small magnetic particles, which bind to CTCs in the blood and pull them out to be detected and counted by specialized equipment.
Patients with five or more CTCs in their blood sample had the worst outcomes. Compared with patients who had no CTCs, they were 3.22 times as likely to die during the study period and 2.46 times as likely to have their cancer progress. They were only 0.26 times as likely to achieve a complete prostate-specific antigen (PSA) response.
In addition, men with five or more CTCs had a median survival of 27.9 months following the blood test, compared with 56.2 months for men with one to four CTCs and at least 78 months for men with no CTCs. Many patients in the latter group survived past the date of publication, so the median survival could not yet be calculated.
Candidates for Clinical Trials
This study shows that measuring CTC counts at the start of therapy may predict long-term survival rates, even in men who go on to receive many treatments for metastatic prostate cancer over a years-long period. Thus, the test may help to identify men early on for trials of new and potentially more aggressive therapies.
“We want to enrich these clinical trials with men who need all that extra help—who really would benefit from three drugs vs just two, or from being on a new chemotherapy drug, even though it may have more side effects,” Dr. Goldkorn said.
Dr. Goldkorn and his team are now testing a new blood test that measures not just CTC counts, but also the molecular composition of CTCs and tumor DNA circulating in the blood as well as other factors. Their goal is to create biomarkers with even more predictive power, which may ultimately help match patients with specific treatment options.
Disclosure: This work was supported by the NCI of the National Institutes of Health [CA172436, CA180888 and CA180819] and Millennium Pharmaceuticals (Takeda). For full disclosure of all study authors, visit JAMA Network Open.
