Prostate-specific Membrane Antigen PET: Therapy Response Assessment in Metastatic Prostate Cancer

Baseline Imaging Derived Factors of Response Following [225Ac]Ac-J591 Therapy in Metastatic Castration-Resistant Prostate Cancer: A Lesion Level Analysis

PURPOSE

Actinium-225 labeled prostate-specific membrane antigen (PSMA) targeted radionuclide therapy has emerged as a potential treatment option in the management of men with metastatic castrate-resistant prostate cancer (mCRPC). This study investigated molecular imaging-derived parameters and compared imaging response of lesions categorized by tumor site.

METHODS

Men with mCRPC treated with [225Ac]Ac-J591 from 2017 to 2022 at our center on two prospective trials (NCT03276572 and NCT04506567) with pre- and post-treatment [68Ga]Ga-PSMA-11 Positron Emission Tomography (PET) imaging studies available were included. SUVpeak of the 3 most- and 3 least-avid lesions of the tumor sites were manually assessed. The median change of the SUVpeak from pre- to post-treatment per tumor site was evaluated using the paired Wilcox test. An objective response (OR) in the follow-up image was defined as complete or partial response using PET Response Criteria in Solid Tumors (PERCIST) 1.0.

RESULTS

A total of 46 cases met the criteria for image review; most of them (n = 25, 54.3%) had more than one tumor site category. In total, 445 PSMA PET-positive lesions were assessed: 220 osseous, 163 nodal, 41 visceral, and 21 prostatic lesions. After treatment with [225Ac]Ac-J591, absolute SUVpeak values per tumor site declined significantly (p < 0.05) except for prostatic lesions (p = 1). The PERCIST-OR rate for osseous, nodal, visceral, and prostatic lesions was 53%, 28%, 56%, and 38%, respectively.

CONCLUSION

[225Ac]Ac-J591 is an active treatment in men with mCRPC. Tumor distribution patterns may influence treatment response and potentially prognosis. Our findings warrant further validation in a larger cohort but may be considered in treatment planning and trial design.

Imaging assessment of prostate cancer recurrence: advances in detection of local and systemic relapse

Prostate cancer (PCa) relapse, defined either by persistent PSA levels (after RP) or biochemical recurrence (BCR), is a common occurrence. The imaging evaluation of patients experiencing PCa relapse has undergone significant advancements in the past decade, notably with the introduction of new Positron Emission Tomography (PET) tracers such as Prostate-specific membrane antigen (PSMA), and the progress in functional Magnetic Resonance Imaging (MRI). This article will explore the role of traditional imaging, the evolution of MRI towards the development of the Prostate Magnetic Resonance Imaging for Local Recurrence Reporting (PI-RR) scoring system, and how next-generation imaging is enhancing diagnostic accuracy in the setting of PCa relapse, which is essential for adopting personalized strategies that may ultimately impact outcomes.

PSMA Radiotheranostics in Prostate Cancer: Principles, Practice, and Future Prospects

Prostate cancer is a leading cause of cancer-related mortality in men, with metastatic castration-resistant prostate cancer presenting a substantial treatment challenge. The authors focuse on prostate-specific membrane antigen (PSMA) radiotheranostics, particularly lutetium 177 (177Lu)-PSMA radioligand therapy, as an emerging treatment modality for metastatic castration-resistant prostate cancer. The U.S. Food and Drug Administration approval of 177Lu-PSMA-617 marked a substantial advancement in the treatment paradigm of metastatic castration-resistant prostate cancer, based on the VISION trial that showed improved overall survival and quality of life compared with those for standard care. PSMA expression, assessed via PSMA PET, is crucial for patient selection and assessment of treatment eligibility. The authors discuss current practices, including therapy administration, dosing, and side effects, with a particular focus on eligibility criteria and the added value of posttherapy imaging. Response assessment criteria using PSMA PET are discussed, although these require further validation. The discussion of future directions highlights ongoing trials investigating PSMA targeting agents, the extension of radioligand therapy to earlier stages of prostate cancer, and combination therapies. This review underscores the role of PSMA radioligand therapy in the evolving landscape of prostate cancer treatment and its promise for improving patient outcomes. ©RSNA, 2024 Supplemental material is available for this article.

Standardized template for clinical reporting of PSMA PET/CT scans

PURPOSE

Accurate diagnosis and staging of prostate cancer are crucial to improving patient care. Prostate-specific membrane antigen (PSMA)-targeted positron emission tomography with computed tomography (PET/CT) imaging has demonstrated superiority for initial staging and restaging in patients with prostate cancer. Referring physicians and PET/CT readers must agree on a consistent communication method and application of information derived from this imaging modality. While several guidelines have been published, a single PSMA PET/CT reporting template has yet to be widely adopted. Based on the consensus from community and academic physicians, we developed a standardized PSMA PET/CT reporting template for radiologists and nuclear medicine physicians to report and relay key imaging findings to referring physicians. The aim was to improve the quality, clarity, and utility of imaging results reporting to facilitate patient management decisions.

METHODS

Based on community and expert consensus, we developed a standardized PSMA PET/CT reporting template to deliver key imaging findings to referring clinicians.

RESULTS

Core category components proposed include a summary of any prior treatment history; presence, location, and degree of PSMA radiopharmaceutical uptake in primary and/or metastatic tumor(s), lesions with no uptake, and incidentally found lesions with positive uptake on PET/CT.

CONCLUSIONS

This article provides recommendations on best practices for standardized reporting of PSMA PET/CT imaging. The generated reporting template is a proposed supplement designed to educate and improve data communication between imaging experts and referring physicians.

Early response monitoring during [177Lu]Lu-PSMA I&T therapy with quantitated SPECT/CT predicts overall survival of mCRPC patients: subgroup analysis of a Swiss-wide prospective registry study

PURPOSE

To assess early tumor response with quantitated SPECT/CT and to correlate it with clinical outcome in metastatic castration-resistant prostate cancer (mCRPC) patients treated with 177Lutetium-PSMA I&T therapy.

METHODS

Single-center, observational study, part of the prospective Swiss national cancer registry study investigating the safety and efficacy of [177Lu]Lu-PSMA I&T (EKNZ: 2021-01271) in mCRPC patients treated with at least two cycles of [177Lu]Lu-PSMA I&T 6-weekly. After the first and second cycle quantitated SPECT/CT (Symbia Intevo, Siemens) was acquired 48 h after injection (three fields of view from head to thigh, 5 s/frame) and reconstructed using xQuant® (48i, 1 s, 10-mm Gauss). Image analysis: The PSMA-positive total tumor volumes (TTV) were semi-automatically delineated using a SUV threshold of 3 with MIMencore® (version 7.1.3, Medical Image Merge Software Inc.). Changes in TTV, highest tumor SUVmax, and total tumor SUVmean between cycles 1 and 2 were calculated and grouped into a) stable or decrease and b) increase. Serum PSA levels were assessed at each therapy cycle and at follow-up until progression or death. Changes in TTV, PSA, SUVmax, and SUVmean were correlated with PSA-progression-free survival (PSA-PFS) and the overall survival (OS) using the Kaplan-Meier methodology (log-rank test).

RESULTS

Between 07/2020 and 04/2022, 111 patients were screened and 73 finally included in the data analysis. The median follow-up was 8.9 months (range 1.4-26.6 months). Stable or decreased TTV at cycle 2 was associated with longer OS (hazard ratio (HR) 0.28, 95% confidence interval (CI) 0.09-0.86, p < 0.01). Similar, stable, or decreased PSA was associated with longer OS (HR 0.21; CI 0.07-0.62, p < 0.01) and PSA-PFS (HR 0.34; 95% CI 0.16-0.72, p < 0.01). Combining TTV and PSA will result in an augmented prognostic value for OS (HR 0.09; CI 0.01-0.63; p < 0.01) and for PSA-PFS (HR 0.11; CI 0.02-0.68; p < 0.01). A reduction of SUVmax or SUVmean was not prognostically relevant, neither for OS (p 0.88 and 0.7) nor for PSA-PFS (p 0.73 and 0.62, respectively).

CONCLUSION

Six weeks after initiating [177Lu]Lu-PSMA I&T, TTV and serum PSA appear to be good prognosticators for OS. Combined together, TTV + PSA change demonstrates augmented prognostic value and can better predict PSA-PFS. Larger studies using TTV change prospectively as an early-response biomarker are warranted for implementing management change towards a more personalized clinical practice.

Prostate-Specific Membrane Antigen PET/Computed Tomography: Pearls and Pitfalls

Prostate-specific membrane antigen PET (PSMA-PET) has emerged as a powerful imaging tool for prostate cancer primary staging, biochemical recurrence, and advanced disease assessment. This article offers a concise overview of the benefits and challenges associated with PSMA-PET for prostate cancer evaluation. The article highlights the advantages of PSMA-PET over conventional imaging, such as its higher sensitivity and specificity for detecting metastases, and the potential for guiding personalized treatment decisions. However, it also explores the limitations and potential pitfalls for interpretation. Overall, the article aims to provide valuable insights for clinicians and diagnostic imaging physicians in clinical practice.

Quantitative [68Ga]Ga-PSMA-11 PET biomarkers for the analysis of lesion-level progression in biochemically recurrent prostate cancer: a multicentre study

[68Ga]Ga-PSMA-11 PET has become the standard imaging modality for biochemically recurrent (BCR) prostate cancer (PCa). However, its prognostic value in assessing response at this stage remains uncertain. The study aimed to assess the prognostic significance of radiographic patient-level patterns of progression derived from lesion-level biomarker quantitation in metastatic disease sites. A total of 138 BCR PCa patients with both baseline and follow-up [68Ga]Ga-PSMA-11 PET scans were included in this analysis. Tumour response was quantified at the lesion level using commonly used quantitative parameters (SUVmean, SUVmax, SUVpeak, volume), and patients were classified as systemic, mixed, or no-progression based on these response classifications. A total of 328 matched lesions between baseline and follow-up scans were analysed. The results showed that systemic progressors had a significantly higher risk of death than patients with no progression with SUVmean demonstrating the highest prognostic value (HR = 5.70, 95% CI = 2.63-12.37, p < 0.001, C-Index = 0.69). Moreover, progressive disease as measured by SUVmean using the radiographic PSMA PET Progression Criteria (rPPP) was found to be significantly prognostic for patient overall survival (HR = 3.67, 95% CI = 1.82-7.39, p < 0.001, C-Index = 0.65). This work provides important evidence supporting the prognostic utility of PSMA response quantitation in the BCR setting.

Oligometastatic Prostate Cancer: Current Status and Future Challenges

In accordance with the spectrum theory of metastatic disease, an oligometastatic clinical state has been proposed as an intermediary step along the natural history of cancer with few (typically 1-3) metastatic lesions identifiable on imaging that may be amenable to metastasis-directed therapy. Effective therapy of oligometastatic disease is anticipated to impact cancer evolution by delaying progression and improving patient outcome at a minimal or acceptable cost of toxicity. There has been increasing recognition of oligometastatic disease in prostate cancer with the advent of new-generation imaging agents, most notably the recently approved PET radiotracers based on targeting prostate-specific membrane antigen. Early clinical trials with metastasis-directed therapy of oligometastases have provided evidence for delaying the employment of systematic therapy and improving outcome in selected patients. Despite these encouraging results, much needs to be investigated and learned about the underlying biology of the oligometastatic state along the evolutionary clinical course of prostate cancer, the identification of relevant imaging and nonimaging predictive and prognostic biomarkers, and the development of treatment strategies to optimize short-term and long-term patient outcome. We provide a review of the current status and the lingering challenges of this rapidly evolving clinical space in prostate cancer.

Sialylated glycoproteins as biomarkers and drivers of progression in prostate cancer

Sialic acids have been implicated in cancer initiation, progression, and immune evasion in diverse human malignancies. Sialylation of terminal glycans on cell surface and secreted glycoproteins is a long-recognized feature of cancer cells. Recently, immune checkpoint inhibitor immunotherapy has tremendously improved the outcomes of patients with various cancers. However, available immunotherapy approaches have had limited efficacy in metastatic castration-resistant prostate cancer. Sialic acid modified glycoproteins in prostate cancers and their interaction with Siglec receptors on tumor infiltrating immune cells might underlie immunosuppressive signaling in prostate cancer. Here, we summarize the function of sialic acids and relevant glycosynthetic enzymes in cancer initiation and progression. We also discuss the possible uses of sialic acids as biomarkers in prostate cancer and the potential methods for targeting Siglec-sialic acid interactions for prostate cancer treatment.

Molecular Imaging Assessment of Androgen Deprivation Therapy in Prostate Cancer

Hormonal therapy has long been recognized as a mainstay treatment for prostate cancer. New generation imaging agents have provided unprecedented opportunities at all phases along the natural history of prostate cancer. We review the literature on the effect of androgens and androgen deprivation therapy on prostate tumor at its various biological phases using the new generation molecular imaging agents in conjunction with positron emission tomography.

Gallium-68 Prostate-Specific Membrane Antigen Positron Emission Tomography: A Practical Guide for Radiologists and Clinicians

Prostate cancer (PCa) is the third most common form of cancer and the most common cancer diagnosis in men in the United States. It is known that prostate-specific membrane antigen (PSMA) is overexpressed in PCa. PSMA is a type II transmembrane glycoprotein expressed in several benign and malignant tissues. In December 2020, FDA approved Gallium-68 (68Ga) PSMA, which is a PSMA-targeted positron emission tomography (PET) imaging agent. Molecular imaging targeting PSMA has shown substantial advancement in PCa imaging. In this article, we discuss the radiopharmaceutical, indications to do PSMA PET, technical aspects of PSMA PET imaging, normal biodistribution of PSMA, other benign and malignant conditions that can take up PSMA, staging of prostate cancer, and how to report PSMA PET.

The Role and Significance of Bioumoral Markers in Prostate Cancer

The prostate is one of the most clinically accessible internal organs of the genitourinary tract in men. For decades, the only method of screening for prostate cancer (PCa) has been digital rectal examination of 1990s significantly increased the incidence and prevalence of PCa and consequently the morbidity and mortality associated with this disease. In addition, the different types of oncology treatment methods have been linked to specific complications and side effects, which would affect the patient's quality of life. In the first two decades of the 21st century, over-detection and over-treatment of PCa patients has generated enormous costs for health systems, especially in Europe and the United States. The Prostate Specific Antigen (PSA) is still the most common and accessible screening blood test for PCa, but with low sensibility and specificity at lower values (<10 ng/mL). Therefore, in order to avoid unnecessary biopsies, several screening tests (blood, urine, or genetic) have been developed. This review analyzes the most used bioumoral markers for PCa screening and also those that could predict the evolution of metastases of patients diagnosed with PCa.

Biomarkers in Prostate-Specific Membrane Antigen Theranostics

Theranostics of prostate cancer (PC) represents a growing area of development of imaging agents and targeted radionuclide therapeutics against a major target, prostate specific membrane antigen (PSMA). In view of the encouraging efficacy from the use of 177Lu and other radionuclides in metastatic castration-resistant prostate cancer (mCRPC), it is becoming increasingly important to identify surrogate markers that can help predict which patients are more likely to respond and experience improved survival. This review discusses potential predictors of efficacy of PSMA-targeted radionuclide therapies (TRT) segregated in three major categories: imaging, clinical and molecular.

General Concepts in Theranostics

Theranostics describes the pairing of diagnostic biomarkers and therapeutic agents with common specific targets. Nuclear medicine is the greatest theranostics protagonist, relying on radioactive tracers for imaging biologic phenomena and delivering ionizing radiation to the tissues that take up those tracers. The concept has gained importance with the growth of personalized medicine, allowing customized management for diseases, refining patient selection, better predicting responses, reducing toxicity, and estimating prognosis. This work provides an overview of the general concepts of the theranostics approach in nuclear medicine discussing its background, features, and future directions in imaging and therapy.

Concordance between Response Assessment Using Prostate-Specific Membrane Antigen PET and Serum Prostate-Specific Antigen Levels after Systemic Treatment in Patients with Metastatic Castration Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Prostate-specific membrane antigen positron emission tomography (PSMA PET) has recently gained interest as a promising tool for treatment response evaluation in metastatic castration-resistant prostate cancer (CRPC). We performed a systematic review and meta-analysis assessing the concordance between response evaluation using PSMA PET and serum prostate-specific antigen (PSA) level after systemic treatment and the association between PSMA PET and overall survival in metastatic CRPC patients. PubMed, Embase, and Cochrane library databases were searched until August 2020. Studies that reported the concordance between PSMA PET and PSA response were included. PSMA PET and PSA response evaluation were dichotomized into response vs. non-response to construct two-by-two contingency tables; an ≥30% increase in PSMA PET according to PET Response Criteria in Solid Tumors 1.0 and as an increase in serum PSA level of ≥25% as per Prostate Cancer Working Group 3 guidelines were defined as non-response. The percent agreement rates were pooled using random-effect model. Ten studies (268 patients) were included. The concordance rates ranged 0.50–0.84 with a pooled proportion of 0.73 (95% confidence interval 0.67–0.79). Patients were treated with ¹⁷⁷Lu-PSMA therapy in five, chemotherapy in three, ²²³Ra in one, and more than one type in one study. Various PET parameters were used: the most widely evaluated was PSMA tumor volume (PSMA-TV). Similar proportions were found across different therapeutic agents, PET response parameters, and regarding directionality of discordance (PSA response/PSMA non-response vs. PSMA response/PSA non-response). Two studies reported that a decrease in PSMA-TV was associated with better overall survival. PSMA PET and PSA response assessments were discordant in nearly a fourth of metastatic CRPC patients. Further studies are warranted to establish the clinical meaning of this discordance and define appropriate management for such clinical situation.