A comparison of prostate cancer bone metastases on 18F-Sodium Fluoride and Prostate Specific Membrane Antigen (18F-PSMA) PET/CT: Discordant uptake in the same lesion

Current and future targeted alpha particle therapies for osteosarcoma: Radium-223, actinium-225, and thorium-227

Osteosarcoma is a high-grade sarcoma characterized by osteoid formation, nearly universal expression of IGF1R and with a subset expressing HER-2. These qualities provide opportunities for the use of the alpha particle-emitting isotopes to provide targeted radiation therapy via alpha particles precisely to bone-forming tumors in addition to IFG1R or Her-2 expressing metastases. This review will detail experience using the alpha emitter radium-223 (²²³Ra, tradename Xofigo), that targets bone formation, in osteosarcoma, specifically related to patient selection, use of gemcitabine for radio-sensitization, and using denosumab to increasing the osteoblastic phenotype of these cancers. A case of an inoperable left upper lobe vertebral-paraspinal-mediastinal osteoblastic lesion treated successfully with ²²³Ra combined with gemcitabine is described. Because not all areas of osteosarcoma lesions are osteoblastic, but nearly all osteosarcoma cells overexpress IGF1R, and some subsets expressing Her-2, the anti-IGF1R antibody FPI-1434 linked to actinium-225 (²²⁵Ac) or the Her-2 antibody linked to thorium-227 (²²⁷Th) may become other means to provide targeted alpha particle therapy against osteosarcoma (NCT03746431 and NCT04147819).

The Continuum of Metastatic Prostate Cancer: Interpreting PSMA PET Findings in Recurrent Prostate Cancer

Conventional imaging has been the standard imaging modality for assessing prostate cancer recurrence and is utilized to determine treatment response to therapy. Molecular imaging with PSMA PET-CT has proven to be more accurate, sensitive, and specific at identifying pelvic or distant metastatic disease, resulting in earlier diagnosis of advanced disease. Since advanced disease may not be seen on conventional imaging, due to its lower sensitivity, but can be identified by molecular imaging, this reveals that metastatic prostate cancer occurs on a continuum from negative PSMA PET-CT and negative conventional imaging to positive PSMA PET-CT and positive conventional imaging. Understanding this continuum, the accuracy of these modalities, and treatment related outcomes based on imaging, will allow the clinician to counsel patients on management. This review will highlight the differences in conventional and molecular imaging in prostate cancer and how PSMA PET-CT can be used for the management of prostate cancer patients in different clinical scenarios, while providing cautionary notes for overtreatment.

More Than Meets the Eye: Scientific Rationale behind Molecular Imaging and Therapeutic Targeting of Prostate-Specific Membrane Antigen (PSMA) in Metastatic Prostate Cancer and Beyond

Simple Summary

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in prostate cancer and correlates with the aggressiveness of the disease. PSMA is a promising target for imaging and therapeutics in prostate cancer patients validated in prospective trials. However, the role of PSMA in prostate cancer progression is poorly understood. In this review, we discuss the biology and scientific rationale behind the use of PSMA and other targets in the detection and theranostics of metastatic prostate cancer.

Abstract

Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

Whole-Body [18F]-Fluoride PET SUV Imaging to Monitor Response to Dasatinib Therapy in Castration-Resistant Prostate Cancer Bone Metastases: Secondary Results from ACRIN 6687

ACRIN 6687, a multi-center clinical trial evaluating differential response of bone metastases to dasatinib in men with metastatic castration-resistant prostate cancer (mCRPC), used [¹⁸F]-fluoride (NaF) PET imaging. We extend previous ACRIN 6687 dynamic imaging results by examining NaF whole-body (WB) static SUV PET scans acquired after dynamic scanning. Eighteen patients underwent WB NaF imaging prior to and 12 weeks into dasatinib treatment. Regional VOI analysis of the most NaF avid bone metastases and an automated whole-body method using Quantitative Total Bone Imaging software (QTBI; AIQ Solutions, Inc., Madison, WI, USA) were used. We assessed differences in tumor and normal bone, between pre- and on-treatment dasatinib, and evaluated parameters in association with PFS and OS. Significant decrease in average SUV_max and average SUV_peak occurred in response to dasatinib. Univariate and multivariate analysis showed NaF uptake had significant association with PFS. Pharmacodynamic changes with dasatinib in tumor bone can be identified by WB NaF PET in men with mCRPC. WB PET has the benefit of examining the entire body and is less complicated than single FOV dynamic imaging.

Prostate-specific Membrane Antigen-based Imaging of Castration-resistant Prostate Cancer

CONTEXT

Positron emission tomography (PET) targeting prostate-specific membrane antigen (PSMA) has unprecedented accuracy for localization of initial or recurrent prostate cancer (PC). There is now growing evidence regarding the value of PSMA-PET in patients with advanced PC.

OBJECTIVE

To review the value of PSMA-PET/computed tomography (CT) in the context of castration-resistant PC (CRPC).

EVIDENCE ACQUISITION

A search of the PubMed database using the terms "PSMA PET castration resistant prostate cancer" (years 2011-2020) was performed. Reviews, case reports/series, non-English articles, preclinical studies, access-restricted studies, and studies on PSMA radioligand therapy without further analysis of PSMA-PET parameters were subsequently excluded.

EVIDENCE SYNTHESIS

Compared to conventional imaging, PSMA-PET better identifies the true extent of CRPC, especially nonmetastatic CRPC. The clinical benefit of this stage migration is still unclear and needs to be evaluated in further studies. High accuracy of PSMA-PET holds promise for better, PET-guided metastasis-directed treatment in patients with oligometastatic CRPC. PSMA-PET is an essential eligibility criterion for [¹⁷⁷Lu]-PSMA theranostic applications. Preliminary evidence indicates the value of PSMA-PET for the assessment of treatment responses.

CONCLUSIONS

Among other applications, PSMA-PET offers more precise staging for nonmetastatic CRPC. In particular, target localization for metastasis-directed therapy and target expression assessment for PSMA radioligand therapy also hold promise. Potential translation of this diagnostic tool into an oncologic benefit needs to be defined in future trials.

PATIENT SUMMARY

This review describes how prostate-specific membrane antigen positron emission tomography (PSMA-PET), a new sensitive imaging tool for prostate cancer, might help to guide clinicians in making treatment decisions for advanced prostate cancer.

Recent updates and developments in PET imaging of prostate cancer

A number of positron emission tomography (PET) radiotracers have been developed to improve the sensitivity and specificity of imaging for prostate cancer. These radiotracers include the bone-seeking agent Na¹⁸F as well as more tumor-specific compounds such as ¹¹C-choline and ¹⁸F-fluciclovine. In this review, we will discuss the advantages and disadvantages of these PET radiotracers for the imaging of men with prostate cancer across a range of clinical contexts. We will also touch upon radiotracers in late clinical development that have not gained regulatory approval, including those targeted against prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR).

Meeting report from the Prostate Cancer Foundation PSMA theranostics state of the science meeting

INTRODUCTION

The Prostate Cancer Foundation (PCF) convened a PCF prostate-specific membrane antigen (PSMA) Theranostics State of the Science Meeting on 18 November 2019, at Weill Cornell Medicine, New York, NY.

METHODS

The meeting was attended by 22 basic, translational, and clinical researchers from around the globe, with expertise in PSMA biology, development and use of PSMA theranostics agents, and clinical trials. The goal of this meeting was to discuss the current state of knowledge, the most important biological and clinical questions, and critical next steps for the clinical development of PSMA positron emission tomography (PET) imaging agents and PSMA-targeted radionuclide agents for patients with prostate cancer.

RESULTS

Several major topic areas were discussed including the biology of PSMA, the role of PSMA-targeted PET imaging in prostate cancer, the physics and performance of different PSMA-targeted PET imaging agents, the current state of clinical development of PSMA-targeted radionuclide therapy (RNT) agents, the role of dosimetry in PSMA RNT treatment planning, barriers and challenges in PSMA RNT clinical development, optimization of patient selection for PSMA RNT trials, and promising combination treatment approaches with PSMA RNT.

DISCUSSION

This article summarizes the presentations from the meeting for the purpose of globally disseminating this knowledge to advance the use of PSMA-targeted theranostic agents for imaging and treatment of patients with prostate cancer.

Understanding and Improving 18F-Fluciclovine PET/CT Reports: A Guide for Physicians Treating Patients with Biochemical Recurrence of Prostate Cancer

The positron emission tomography (PET) tracer ¹⁸F-fluciclovine has seen increasing use to localize disease in men with biochemical recurrence of prostate cancer, i.e., elevated prostate-specific antigen (PSA) levels post-treatment. ¹⁸F-Fluciclovine PET/computed tomography (CT) imaging reports now play central roles in many physician-patient discussions. However, because no standardized grading system or templates yet exist for ¹⁸F-fluciclovine image assessment, reports vary in format, comprehensiveness, and terminology and may be challenging to fully understand. To better utilize these documents, referring physicians should be aware of six key features of ¹⁸F-fluciclovine PET/CT. First, ¹⁸F-fluciclovine is a radiolabeled synthetic amino acid targeting the amino acid transporters ASCT2 and LAT1, which are ubiquitous throughout the body, but overexpressed in prostate cancer. Second, ¹⁸F-fluciclovine image interpretation is predominantly visual/qualitative: radiotracer uptake in suspicious lesions is compared with uptake in bone marrow or blood pool. Location of ¹⁸F-fluciclovine-avid lesions relative to typical recurrence sites and findings elsewhere in the patient are considered when evaluating lesions' probability of malignancy, as is visibility on maximum intensity projection images when assessing bone lesions. Third, ¹⁸F-fluciclovine PET/CT detection rates increase as PSA levels rise. Fourth, detection rates may differ among centers, possibly due to equipment and reader experience. Fifth, since no diagnostic test is 100% accurate, scan data should not be used in isolation. Lastly, ¹⁸F-fluciclovine PET/CT findings frequently induce changes in disease management plans. In the prospective multicenter LOCATE and FALCON studies, scans altered management plans in 59% (126/213) and 64% (66/104) of patients, respectively; 78% (98/126) and 65% (43/66) of changes, respectively, involved modality switches. Referring physicians and imagers should collaborate to improve scan reports. Referrers should clearly convey critical information, including prescan PSA levels, and open clinical questions. Imagers should produce reports that read like consultations, avoid leaving open questions, and if needed, provide thoughts on next diagnostic steps.

Systemic Treatment of Bone Disease in Metastatic Urinary Malignancies

CONTEXT

Bone metastasis is a common site of metastatic disease in patients with genitourinary malignancies. Given that the presence of bone metastasis decreases survival and has a negative impact on quality of life impact, it is critical to optimize management of this patient population.

OBJECTIVE

To systematically review literature on the systemic treatment of bone metastasis in prostate cancer, renal cell carcinoma, urothelial carcinoma, and germ cell tumors.

EVIDENCE ACQUISITION

We performed a nonsystematic critical review of PubMed/Medline, clinicaltrials.gov, and the Cochrane Library from January 2001 to February 2019. Identified reports were reviewed according to the Consolidated Standards of Reporting Trials, and selected based on reporting skeletal related events and symptomatic skeletal events for patients with urologic malignancies.

EVIDENCE SYNTHESIS

Skeletal metastases occur frequently in genitourinary malignancies, at rates around 80% for patients with metastatic prostate cancer and 30% for patients with metastatic renal cell and urothelial carcinoma, and are uncommon in patients with germ cell tumors. Skeletal related events and symptomatic skeletal events can occur in these patients. Optimization of bone health involves dietary and lifestyle modifications, and use of osteoclast-targeted agents in select individuals. Additionally, disease-modifying agents, such as radiopharmaceutical, immunotherapy, and cMET inhibitors, which have activity in the bone, have improved outcomes for patients, including skeletal-related events and symptomatic skeletal events.

CONCLUSIONS

While the presence of bone metastases is associated with increased mortality and worse outcomes in patients with genitourinary malignancies, strategies have been developed to improve quality of life and survival for patients with skeletal metastases. Future studies investigating novel therapeutic options and bone supporting agents are warranted to target this patient population.

PATIENT SUMMARY

In this report, we reviewed the current literature and recent clinical trials involving treatment of bone metastases in urinary cancers. The use of bone-targeting agents can improve outcomes for patients, and additional lifestyle modification can optimize bone health in this population.