Early Blood Test Predicts Survival in Patients with Metastatic Prostate Cancer

By LabMedica International staff writers
Posted on 08 Oct 2024

Image: The CELLSEARCH System is the first and only clinically validated, FDA-cleared system for identification, isolation, and enumeration of CTCs from a simple blood test (Photo courtesy of Menarini, Inc.)

Before prostate cancer spreads, it can be effectively treated with surgery or radiation. However, once the cancer metastasizes and becomes incurable, systemic treatments are used to extend survival as much as possible. Biomarkers that predict patient responses to these treatments could enable better personalization of care, but such markers are rare. Now, a new blood test, conducted when metastatic prostate cancer is first diagnosed, can predict which patients are most likely to respond to treatment and have the longest survival rates. This test can help clinicians determine which patients should receive standard treatments and who might benefit from more aggressive and experimental drug trials.

A recent study demonstrated that measuring circulating tumor cells (CTCs), which are rare cancer cells shed from tumors into the bloodstream, is a reliable method to predict future treatment responses and survival outcomes. Although CTCs have been studied in later stages of prostate cancer, this was the first time researchers at the USC Norris Comprehensive Cancer Center (Los Angeles, CA, USA) assessed whether CTC counts at the initial diagnosis of metastatic prostate cancer can predict long-term survival or treatment progression. The researchers used Menarini's (Bologna, Italy) CellSearch, an FDA-cleared liquid biopsy technology, to detect and measure CTCs in blood samples. CellSearch utilizes immunomagnetic beads, with antibodies attached to magnetic particles, to bind to CTCs in the blood and isolate them for detection and counting by specialized equipment.

The research, published in JAMA Network Open, revealed that patients with five or more CTCs in their blood samples had the poorest outcomes. Compared to patients with zero CTCs, they were 3.22 times more likely to die during the study and 2.46 times more likely to experience cancer progression. They were also significantly less likely—0.26 times—to achieve a complete prostate-specific antigen (PSA) response, indicating a poor treatment response. Men with five or more CTCs had a median survival of 27.9 months after the blood test, compared to 56.2 months for those with one to four CTCs, and at least 78 months for men with zero CTCs. The findings indicated that higher CTC counts were associated with shorter survival, faster disease progression, and a weaker response to standard treatments.

This study highlights that measuring CTC counts at the onset of therapy can predict long-term survival, even for men who undergo multiple treatments over several years for metastatic prostate cancer. The test could help identify candidates early for trials of newer, potentially more aggressive therapies. The researchers believe that the widely available CellSearch blood test could quickly flag patients who are unlikely to respond to standard treatment, potentially guiding them toward more intensive therapies, including clinical trials of new drugs with higher risks but possible survival benefits for high-risk patients. The team is now working on a new blood test that not only counts CTCs but also analyzes their molecular composition, tumor DNA circulating in the blood, and other factors. Their goal is to develop even more predictive biomarkers to better match patients with tailored treatment options.

“You couldn’t tell these men apart when they walked through the door,” said Amir Goldkorn, MD, lead author of the study and associate director of translational sciences at the USC Norris Comprehensive Cancer Center. “All of their other variables and prognostic factors were seemingly the same, and yet they had very, very different outcomes over time. 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.”