A simple blood test performed at the time of diagnosis for metastatic prostate cancer can predict how well patients will respond to treatment and their overall survival. This test helps doctors determine which patients should receive standard treatment and which might benefit from more aggressive new drug trials.
The study, a Phase III clinical trial, was published in JAMA Network Open. It highlights the potential of measuring circulating tumor cells (CTCs) to predict treatment response and survival prospects reliably. CTCs are rare cancer cells that tumors shed into the bloodstream.
Predicting Treatment Response
Researchers, led by Dr. Amir Goldkorn from the USC Norris Comprehensive Cancer Center, found that men with higher blood levels of CTCs had shorter median survival times and a greater risk of death during the study period. Their disease could only be controlled by treatment for a shorter time.
"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 Dr. Goldkorn.
The researchers used CellSearch, an FDA-cleared blood test already widely available, to identify patients unlikely to respond to standard treatment.
Study Details and Findings
The research was part of a Phase III clinical trial by the SWOG Cancer Research Network, involving 503 men with metastatic prostate cancer. Baseline blood samples were analyzed to measure CTC levels.
Patients with five or more CTCs in their blood sample had the poorest outcomes. They were more than three times as likely to die during the study period than patients with no CTCs and nearly 2.5 times more likely to see their cancer progress.
Men with five or more CTCs lived a median of 27.9 months after their blood test, compared to 56.2 months for men with one to four CTCs and at least 78 months for men with none.
Implications for Treatment
The study indicates that measuring CTC counts at the start of therapy can predict long-term survival rates. This allows for early identification of men who may benefit from 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 versus just two, or from being on a new chemotherapy drug, even though it may have more side effects," Dr. Goldkorn explained.
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, aiming to create biomarkers with even more predictive power to match patients with specific treatment options.
