By Gilang Cahya 
A groundbreaking study conducted by researchers at the UCLA Health Jonsson Comprehensive Cancer Center has revealed that a significant proportion of men diagnosed with high-risk, nonmetastatic hormone-sensitive prostate cancer may, in fact, have advanced disease that has spread beyond the prostate. This finding, published in the esteemed journal JAMA Network Open, challenges current diagnostic paradigms and underscores the critical role of advanced imaging techniques in accurately staging prostate cancer, a crucial step that directly influences treatment decisions and patient prognoses.
Redefining Staging: The Power of PSMA-PET Imaging
The study’s most striking revelation is that nearly half of high-risk prostate cancer patients, who were classified as nonmetastatic based on conventional imaging methods, actually exhibit metastatic disease when assessed using advanced prostate-specific membrane antigen-positron emission tomography (PSMA-PET) imaging. This suggests that traditional imaging modalities, such as CT scans and bone scans, may be systematically underestimating the extent of cancer spread in a substantial number of patients.
Dr. Jeremie Calais, a senior author of the study, director of the Ahmanson Translational Theranostics Division’s clinical research program, and associate professor at the department of molecular and medical pharmacology at the David Geffen School of Medicine at UCLA, emphasized the study’s implications. "Our study demonstrates the critical role of PSMA-PET in accurately staging prostate cancer, which can significantly impact treatment decisions and outcomes," Dr. Calais stated. "This advanced imaging technology is fundamentally changing how we approach prostate cancer staging, offering a more precise picture of disease extent."
PSMA-PET imaging operates on a different principle than conventional anatomical imaging. It utilizes minute quantities of radioactive tracers, specifically designed to bind to prostate-specific membrane antigen (PSMA), a protein that is highly expressed on the surface of prostate cancer cells. These radiotracers, when injected into the bloodstream, accumulate in areas where prostate cancer cells are present, making these sites visible on PET scans. Unlike conventional imaging, which primarily provides structural information about organs and tissues, PSMA-PET offers functional imaging that highlights the biological activity of the cancer. This functional insight is invaluable for detecting even small clusters of metastatic cells that might be missed by traditional methods.
The EMBARK Trial and the Need for Reevaluation
The impetus for this retrospective study stemmed from observations regarding the clinical adoption of PSMA-PET. While this advanced imaging has become increasingly integrated into clinical practice, many pivotal clinical trials that have shaped current treatment guidelines, including the landmark EMBARK trial, did not incorporate PSMA-PET for patient selection. This means that the patient populations studied in these trials may not accurately reflect the true disease burden as understood by today’s advanced imaging capabilities.
The EMBARK trial, a large, randomized, placebo-controlled study, previously demonstrated that adding enzalutamide, a potent androgen deprivation therapy (ADT) hormone therapy, to standard ADT significantly improved metastasis-free survival in men with high-risk recurrent prostate cancer. However, the eligibility criteria for the EMBARK trial relied on conventional imaging to define patients as having disease confined to the prostate or pelvic lymph nodes, with no evidence of distant metastases. Researchers hypothesized that this reliance on older imaging techniques might have inadvertently included patients with occult metastases, thereby potentially affecting the interpretation of the trial’s outcomes.
To investigate this hypothesis, the UCLA team conducted a post hoc analysis of 182 patients who were part of the EMBARK trial cohort. These patients had high-risk recurrent prostate cancer and were initially deemed eligible for the trial, meaning conventional imaging suggested their disease was limited. The researchers then re-evaluated these patients using PSMA-PET imaging to compare the findings with the original diagnostic assessments.
Striking Discrepancies Revealed by PSMA-PET
The results of this comparative analysis were profound. The PSMA-PET scans detected cancer metastases in a staggering 46% of patients who had previously been classified as nonmetastatic by conventional imaging. This indicates that almost half of the patients in this carefully selected cohort, considered to have localized disease, actually had cancer that had spread.
Furthermore, the study revealed a significant number of these newly identified metastatic lesions. A substantial 24% of the patients exhibited five or more metastatic lesions that had been completely missed by conventional imaging. This highlights not only the increased sensitivity of PSMA-PET but also its ability to detect a more extensive disease burden than previously appreciated.
Dr. Adrien Holzgreve, a visiting assistant professor at the David Geffen School of Medicine and the first author of the study, expressed his surprise at the magnitude of the findings. "We anticipated that PSMA-PET would detect more suspicious findings compared to conventional imaging," Dr. Holzgreve commented. "However, it was informative to uncover such a high number of metastatic findings in a well-defined cohort of patients resembling the EMBARK trial population that was supposed to only include those without metastases. This strongly suggests that traditional staging methods are insufficient for a significant subset of these patients."
Implications for Clinical Trials and Treatment Strategies
These findings carry significant implications for the design and interpretation of future prostate cancer clinical trials. The study strongly supports the inclusion of PSMA-PET imaging for patient selection in upcoming major industry-sponsored clinical trials. By accurately identifying patients with metastatic disease at an earlier stage, trials can be more precisely designed to evaluate treatments for specific disease states, leading to more reliable and interpretable results.
Moreover, the study compels a reevaluation of current treatment strategies for patients with high-risk nonmetastatic prostate cancer. If a significant proportion of these patients already have metastatic disease, then treatments designed for localized cancer may be suboptimal or even inappropriate. The identification of previously undetected metastases opens the door to potentially more aggressive and effective treatment options, such as targeted radiotherapy, which can deliver high doses of radiation directly to cancerous lesions, both within and outside the prostate.
The integration of new imaging technologies like PSMA-PET into standard care also raises important questions about healthcare economics, physician training, and patient access. Ensuring equitable access to these advanced diagnostic tools will be crucial to realizing their full potential in improving patient outcomes across the board.
The Path Forward: Continued Research and Personalized Therapy
While the current findings underscore the immense potential of PSMA-PET, researchers acknowledge that further investigation is necessary to fully understand its impact on long-term patient outcomes. Dr. Calais noted that ongoing studies are crucial to exploring the broader applications of PSMA-PET and how it can best guide therapeutic interventions.
"We have good rationales to assume that it is helpful to primarily rely on PSMA-PET findings," stated Dr. Holzgreve. "But more high-quality prospective data would be needed to claim superiority of PSMA-PET for treatment-guidance in terms of patient outcome. However, we are confident PSMA-PET will continue to advance prostate cancer staging and guide personalized therapies."
UCLA is actively engaged in further research to address these questions. Current efforts include analyzing follow-up data from four UCLA-led trials to assess how PSMA-PET findings have influenced treatment decisions and, critically, patient outcomes. This prospective data will be vital in establishing the real-world clinical utility of PSMA-PET.
In addition, the UCLA team is participating in an international consortium that is examining over 6,000 patients to investigate the prognostic value of PSMA-PET. By analyzing a large and diverse patient population, researchers aim to determine how PSMA-PET findings correlate with disease progression, treatment response, and overall survival. This collaborative approach is essential for building a robust evidence base that can inform clinical guidelines and ultimately improve the lives of men diagnosed with prostate cancer.
The evolving landscape of prostate cancer diagnostics, propelled by innovations like PSMA-PET, signals a promising future for more precise staging, personalized treatment selection, and ultimately, improved outcomes for patients worldwide. The UCLA study serves as a critical waypoint in this journey, highlighting the urgent need to adapt diagnostic standards to leverage the power of advanced imaging technologies.
