By Gilang Cahya 
A groundbreaking study led by researchers at the UCLA Health Jonsson Comprehensive Cancer Center has revealed that a substantial proportion of men diagnosed with high-risk, nonmetastatic hormone-sensitive prostate cancer may actually have more advanced disease than previously understood. This finding, driven by the application of advanced prostate-specific membrane antigen-positron emission tomography (PSMA-PET) imaging, suggests that conventional imaging techniques may be significantly underestimating the extent of cancer spread in a critical patient population.
Rethinking Prostate Cancer Staging with PSMA-PET
The study, published in the esteemed journal JAMA Network Open, analyzed data from 182 patients with high-risk recurrent prostate cancers who were initially believed to have disease confined to the prostate and were candidates for the influential EMBARK clinical trial. The EMBARK trial, a landmark study that demonstrated the significant benefits of combining enzalutamide, a potent hormone therapy, with androgen deprivation therapy (ADT) in improving metastasis-free survival, relied on traditional imaging modalities for patient selection. However, the UCLA-led research team hypothesized that these conventional methods might not be sensitive enough to detect the subtle spread of cancer in all cases.
The results of the post hoc, retrospective cross-sectional study were striking. When these patients were re-evaluated using PSMA-PET imaging, a remarkable 46% showed evidence of metastatic disease that had been missed by conventional imaging. Even more concerning, 24% of these patients exhibited five or more distinct lesions not identified by standard scans. This suggests a significant discrepancy between the perceived stage of the cancer and its actual biological reality.
"Our study demonstrates the critical role of PSMA-PET in accurately staging prostate cancer, which can significantly impact treatment decisions and outcomes," stated Dr. Jeremie Calais, senior author of the study and 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. "We anticipated that PSMA-PET would detect more suspicious findings compared to conventional imaging. 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," added Dr. Adrien Holzgreve, a visiting assistant professor at the David Geffen School of Medicine and the study’s first author.
The Power of PSMA-PET Imaging
PSMA-PET imaging represents a significant leap forward in visualizing prostate cancer. It utilizes minute quantities of radioactive "tracers," known as radiotracers, that are specifically designed to bind to prostate-specific membrane antigen (PSMA), a protein that is highly expressed on the surface of prostate cancer cells, including metastatic ones. Once bound, these radiotracers emit signals that are detected by a PET scanner, creating detailed images that highlight the location and extent of cancerous activity.
Unlike conventional imaging techniques such as CT scans or bone scans, which primarily provide anatomical information about the size and location of tumors, PSMA-PET offers functional imaging. This means it reveals the biological characteristics of the cancer, such as its metabolic activity and the presence of PSMA, providing a more nuanced and accurate picture of the disease’s spread. This functional insight is crucial for precise staging, which directly influences treatment planning.
The clinical adoption of PSMA-PET has already begun to reshape the landscape of prostate cancer diagnostics. However, a significant challenge has been that many pivotal clinical trials, including the EMBARK trial, were designed and conducted before the widespread availability and integration of PSMA-PET for patient selection. This raises questions about whether the patient populations enrolled in these trials accurately reflected the true spectrum of disease at the time of enrollment, particularly for high-risk individuals.
Unpacking the EMBARK Trial and its Implications
The EMBARK trial, initiated in 2013, enrolled over 1,000 men with metastatic hormone-sensitive prostate cancer. Its primary endpoint was metastasis-free survival, and it demonstrated that adding enzalutamide to ADT significantly delayed the development of detectable metastases or death. The trial was a cornerstone in establishing the benefits of intensified hormone therapy for this patient group.
However, the UCLA study’s findings cast a new light on the patient selection criteria used in trials like EMBARK. If a substantial number of patients classified as "nonmetastatic" by conventional imaging actually harbored microscopic metastases detectable by PSMA-PET, it implies that some patients in these trials may have had more advanced disease than initially presumed. This could potentially:
- Underestimate the true efficacy of treatments: If a treatment is given to patients with more advanced disease than intended, its observed benefit might appear less pronounced than if it had been administered to a truly nonmetastatic population.
- Influence the interpretation of trial results: The observed outcomes in trials that did not utilize PSMA-PET for staging might need to be re-examined in light of this new understanding of disease dissemination.
- Affect eligibility for potentially curative therapies: Patients with localized disease are often candidates for more aggressive, potentially curative treatments like radical prostatectomy or radiation therapy. If their disease is actually metastatic, they might be unnecessarily denied these options or conversely, might be offered treatments that are not optimally suited for their true stage.
The UCLA researchers’ retrospective analysis of patients who met the EMBARK trial’s inclusion criteria, but were then imaged with PSMA-PET, provides compelling evidence for this concern. The fact that nearly half of these "nonmetastatic" patients showed signs of spread highlights a critical gap in diagnostic accuracy.
Broader Impact and Future Directions
The implications of these findings extend far beyond the re-evaluation of past clinical trials. They underscore the urgent need to integrate PSMA-PET imaging into the standard of care for staging high-risk prostate cancer. This shift could lead to:
- More accurate treatment decisions: By providing a clearer picture of the cancer’s extent, PSMA-PET can help oncologists select the most appropriate treatment strategy. For patients with detected metastases, this might involve systemic therapies or even targeted radiotherapy, such as PSMA-targeted radioligand therapy, which has shown promise in treating metastatic prostate cancer.
- Improved patient outcomes: Earlier and more accurate detection of metastases can lead to timelier intervention, potentially slowing disease progression and improving overall survival and quality of life.
- Enhanced clinical trial design: Future clinical trials investigating new prostate cancer therapies should incorporate PSMA-PET for more precise patient stratification, ensuring that trial results are robust and generalizable to the intended patient populations.
"These results challenge the interpretation of previous studies, like the EMBARK trial, and support the inclusion of PSMA-PET for patient selection in clinical and trial interventions in prostate cancer in future major industry-sponsored clinical trials," the study authors concluded. "It also highlights the need to reevaluate treatment strategies and opens the door to potentially curative options for some patients, such as targeted radiotherapy, while raising important questions about integrating new imaging technologies into standard care."
The UCLA team is actively pursuing further research to solidify these findings and explore the full potential of PSMA-PET. Ongoing efforts include analyzing follow-up data from four UCLA trials to meticulously assess how PSMA-PET findings have influenced treatment decisions and subsequent patient outcomes. Furthermore, as part of a large-scale international consortium involving over 6,000 patients, the researchers are investigating the prognostic value of PSMA-PET – its ability to predict how a patient’s cancer will behave over time.
"We have good rationales to assume that it is helpful to primarily rely on PSMA-PET findings," Dr. Holzgreve stated. "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."
A New Era in Prostate Cancer Management
The evolution of medical imaging technology has consistently been a driving force in improving patient care. The advent and increasing sophistication of PSMA-PET imaging represent a pivotal moment in the management of prostate cancer. This UCLA-led study serves as a critical call to action, urging the medical community to embrace these advanced diagnostic tools to ensure that patients receive the most accurate staging and, consequently, the most effective and personalized treatment possible. As research continues to illuminate the full capabilities of PSMA-PET, its integration into routine clinical practice is poised to redefine the standard of care for high-risk prostate cancer, offering renewed hope for better outcomes and a more precise approach to battling this complex disease.
