Hematologic safety of 177Lu-PSMA-617 radioligand therapy in patients with metastatic castration-resistant prostate cancer

Elevated Baseline Mean Corpuscular Volume Predicts the Development of Severe Hematologic Toxicity After 177Lu-DOTATATE Therapy

177Lu-DOTATATE is an effective second-line treatment for metastatic or nonresectable neuroendocrine tumors. This treatment can result in hematologic severe adverse reactions (SARs). Preemptive identification of patients at risk of SARs could mitigate this risk and improve treatment safety and outcomes. Methods: Demographic and oncologic history, pretreatment laboratory values, and SAR frequency were obtained for 126 sequential patients treated with 177Lu-DOTATATE. Univariable and multivariable logistic regression models identified factors correlating with SARs. Results: Relative pretreatment anemia, leukopenia, thrombocytopenia, and elevated mean corpuscular volume (MCV) were significantly correlated with SARs, with an odds ratio of 16 (95% CI, 5-65) in patients with an MCV greater than 95 fL. Conclusion: Pretreatment bone marrow dyscrasias, including an MCV greater than 95 fL, may predict patients at risk for SARs when treated with 177Lu-DOTATATE. Further study is needed to determine whether the risks of SARs outweigh the benefit in these patients.

Optimization Strategies in CAR T-cell Therapy: A Comprehensive Evaluation of Cytopenia, HLH/MAS, and Other Adverse Events

Chimeric antigen receptor (CAR) T-cell therapy has emerged as a transformative treatment for various hematological malignancies. Still, its remarkable efficacy is accompanied by unique adverse events that must be carefully managed. This comprehensive literature review evaluates the safety profile of CAR T-cell therapy, focusing on cytopenia, hemophagocytic lymphohistiocytosis (HLH)/macrophage activation syndrome (MAS), and other potential complications. Cytopenia, characterized by reduced blood cell counts, affects a significant proportion of patients, with rates of anemia, neutropenia, and thrombocytopenia reaching up to 60%, 70%, and 80%, respectively. Risk factors include high tumor burden, prior chemotherapy, and bone marrow involvement. Cytokine release syndrome (CRS) occurs in 13% to 77% of patients and is linked to the cytokine storm induced by CAR T cells, target antigen expression, and preexisting immune dysregulation. Other notable adverse events discussed are cytokine release syndrome, neurotoxicity, and infections. Understanding the mechanisms, risk factors, and management strategies for these adverse events is crucial for optimizing patient outcomes and unlocking the full potential of this revolutionary therapy. The review highlights the need for continued research, interdisciplinary collaboration, and evidence-based approaches to enhance the safety and efficacy of CAR T-cell therapy.

Hematological and renal toxicity in mice after three cycles of high activity [177Lu]Lu-PSMA-617 with or without human α1-microglobulin

Radioligand therapy with [177Lu]Lu-PSMA-617 can be used to prolong life and reduce tumor burden in terminally ill castration resistant prostate cancer patients. Still, accumulation in healthy tissue limits the activity that can be administered. Therefore, fractionated therapy is used to lower toxicity. However, there might be a need to reduce toxicity even further with e.g. radioprotectors. The aim of this study was to (i). establish a preclinical mouse model with fractionated high activity therapy of three consecutive doses of 200 MBq [177Lu]Lu-PSMA-617 in which we aimed to (ii). achieve measurable hematotoxicity and nephrotoxicity and to (iii). analyze the potential protective effect of co-injecting recombinant α1-microglobulin (rA1M), a human antioxidant previously shown to have radioprotective effects. In both groups, three cycles resulted in increased albuminuria for each cycle, with large individual variation. Another marker of kidney injury, serum blood urea nitrogen (BUN), was only significantly increased compared to control animals after the third cycle. The number of white and red blood cells decreased significantly and did not reach the levels of control animals during the experiment. rA1M did reduce absorbed dose to kidney but did not show significant protection here, but future studies are warranted due to the recent clinical studies showing a significant renoprotective effect in patients.

Intermittent Radioligand Therapy with 177Lu-PSMA-617 for Oligometastatic Castration-Resistant Prostate Cancer

177Lu-PSMA-617 radioligand therapy (177Lu-PSMA-RLT) in patients with metastatic castration-resistant prostate cancer (mCRPC) currently consists of 4-6 cycles of 6.0-7.4 GBq of 177Lu-PSMA-617 each every 6-8 weeks. While safety and efficacy could be demonstrated in larger prospective trials irrespective of the tumor burden at 177Lu-PSMA RLT initiation, increased renal absorbed doses due to a reduced tumor sink effect in early responding, oligometastatic mCRPC patients pose difficulties. Response-adapted, dose distributing, intermittent treatment with up to six cycles has not been routinely performed, due to concerns about the potential loss of disease control. Treatment was discontinued in 19 early-responding patients with oligometastatic tumor burden after two (IQR 2-3) cycles of 177Lu-PSMA-RLT and 6.5 ± 0.7 GBq per cycle and resumed upon 68Ga-PSMA-11-PET/CT-based progression (according to the PCWG3 criteria). Subsequent treatment breaks were imposed if a PSMA-based imaging response could be achieved. A total of five (IQR 3-6) cycles reaching a cumulative activity of 32 ± 11 GBq were applied. A routine blood work-up including blood counts and liver and renal function was measured throughout the 177Lu-PSMA-RLT and follow-up to grade toxicity according to CTCAE v5.0 criteria. Survival outcome was calculated based on the Kaplan-Meier method. In total, treatment-free periods of 9 (IQR 6-17) cumulative months and the application of 177Lu-PSMA-RLT cycles over 16 (IQR 9-22) months could be achieved. Fifteen (84%) patients responded to subsequent cycles after the first treatment break and in 7/19 (37%) patients, intermittent 177Lu-PSMA-RLT consisted of ≥2 treatment breaks. The median PFS was 27 months (95% CI: 23-31) and overall survival was 45 months (95% CI: 28-62). No grade ≥3 hematological or renal toxicities could be observed during the 45 ± 21 months of follow-up. The cumulative mean renal absorbed dose was 16.7 ± 8.3 Gy and 0.53 ± 0.21 Gy/GBq. Intermittent radioligand therapy with 177Lu-PSMA-617 is feasible in early-responding patients with oligometastatic disease. A late onset of progression after subsequent cycles and the absence of significant toxicity warrants further investigation of the concept of intermittent treatment in selected patients.

PSMA-targeted therapy for non-prostate cancers

Radioligand therapy (RLT) agents are demonstrating a crucial role in the clinical approach to aggressive malignancies such as metastatic castrate-resistant prostate cancer (m-CRPC). With the recent FDA approval of prostate-specific membrane antigen (PSMA)-targeted RLT for m-CRPC, the field has broadened its gaze to explore other cancers that express PSMA in the tumor parenchyma or tumor neovasculature. In this review article, we discuss current progress in the clinical use of PSMA RLTs in non-prostate cancers such salivary gland cancers, renal cell carcinoma, high grade glioma, and soft tissue sarcoma. We highlight early reports in small case series and clinical trials indicating promise for PSMA-targeted RLT and highlighting the importance of identifying patient cohorts who may most benefit from these interventions. Further study is indicated in non-prostate cancers investigating PSMA RLT dosimetry, PSMA PET/CT imaging as a biomarker, and assessing PSMA RLT safety and efficacy in these cancers.

Adoption of Lutetium-177 PSMA radioligand therapy for metastatic castration resistant prostate cancer: a total population analysis in Germany from 2016 to 2020

PURPOSE

This study is to investigate the adoption and current trends of Lutetium-177 PSMA RLT for mCRPC in Germany.

METHODS

We analyzed data from the reimbursement.INFO tool based on German hospitals' quality reports for Lutetium-177 PSMA RLT from 2016 to 2020 and from the nationwide German hospital billing database (Destatis) for general therapy with open radionuclides in combination with prostate cancer from 2006 to 2020. For validation of these billing data, we included the 177Lu-PSMA RLT cycles from two participating institutions from 2016 to 2020. For detection of trends over time we applied linear regression models.

RESULTS

General therapy with open radionuclides increased from 2006 to 2020. We identified a total of 12,553 177Lu-PSMA RLT cycles. The number of 177Lu-PSMA RLTs steadily increased from a total of 1026 therapies in 2016 to 3328 therapies in 2020 (+ 576 RLT/year; p < 0.005). In 2016, 25 departments of nuclear medicine offered this treatment, which increased to 44 nuclear medicine departments in 2020. In 2016, 16% of nuclear medicine departments (4/25) performed more than 100 177Lu-PSMA RLTs, which increased to 36% (16/44) in 2020 (p < 0.005). In 2016, 88% (22/25) of 177Lu-PSMA RLTs were performed at a university hospital, which decreased to 70% (31/44) in 2020. The proportion of patients older than 65 years receiving 177Lu-PSMA RLT increased from 78% in 2016 to 81% in 2020.

CONCLUSION

Treatment of mCRPC with 177Lu-PSMA RLT has been rapidly increasing in Germany in the recent years providing an additional therapy option. This development is remarkable, because of outstanding formal EMA approval.

Safety and Therapeutic Optimization of Lutetium-177 Based Radiopharmaceuticals

Peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (¹⁷⁷Lu) based radiopharmaceuticals has emerged as a therapeutic area in the field of nuclear medicine and oncology, allowing for personalized medicine. Since the first market authorization in 2018 of [¹⁷⁷Lu]Lu-DOTATATE (Lutathera®) targeting somatostatin receptor type 2 in the treatment of gastroenteropancreatic neuroendocrine tumors, intensive research has led to transfer innovative ¹⁷⁷Lu containing pharmaceuticals to the clinic. Recently, a second market authorization in the field was obtained for [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto®) in the treatment of prostate cancer. The efficacy of ¹⁷⁷Lu radiopharmaceuticals are now quite well-reported and data on the safety and management of patients are needed. This review will focus on several clinically tested and reported tailored approaches to enhance the risk-benefit trade-off of radioligand therapy. The aim is to help clinicians and nuclear medicine staff set up safe and optimized procedures using the approved ¹⁷⁷Lu based radiopharmaceuticals.

Incorporating radioligand therapy in clinical practice in the United States for patients with prostate cancer

Prostate cancer (PC) is the second most commonly diagnosed cancer in the United States. Advanced PC evolves to metastatic castration-resistant PC (mCRPC). Theranostics combining prostate-specific membrane antigen-targeted positron emission tomography imaging and radioligand therapy (RLT) represents a precision medicine approach to PC treatment. With the recent approval of lutetium Lu 177 (¹⁷⁷Lu) vipivotide tetraxetan for men with mCRPC, the utilization of RLT will increase. In this review, we suggest a framework for incorporating RLT for PC into clinical practice. A search of PubMed and Google Scholar was performed using keywords related to PC, RLT, prostate-specific membrane antigen, and novel RLT centers. The authors also provided opinions based on their clinical experience. The setup and operation of an RLT center requires the diligence and cooperation of a well-trained multidisciplinary team committed to patient safety and clinical efficacy. Administrative systems should ensure that treatment scheduling, reimbursement, and patient monitoring are efficient. For optimal outcomes, the clinical care team must have an organizational plan that delineates the full range of required tasks. Establishing new RLT centers for treatment of PC is possible with appropriate multidisciplinary planning. We provide an overview of the key elements to consider when establishing a safe, efficient, and high-quality RLT center.

Extended therapy with [177Lu]Lu-PSMA-617 in responding patients with high-volume metastatic castration-resistant prostate cancer

PURPOSE

The currently used scheme for radioligand therapy (RLT) of patients with metastatic castration-resistant prostate cancer (mCRPC) consists of 4-6 cycles of 6.0-7.4 GBq [¹⁷⁷Lu]Lu-PSMA-617 each. This standard treatment scheme has proved safe and effective resulting in objective response in most patients with no significant toxicity. Many patients, however, show high-volume residual tumor burden after the sixth cycle and may benefit from treatment continuation. Extended treatment with additional cycles has been withheld due to concerns on potential increased toxicity.

METHODS

Twenty-six patients with high-volume residual tumor burden (according to CHAARTED) after standard RLT with [¹⁷⁷Lu]Lu-PSMA-617 and no alternative treatment option received additional RLT cycles reaching a median of 10 (range 7-16) cycles with a mean activity of 7.4 ± 0.9 GBq per cycle. Response assessment with [⁶⁸Ga]Ga-PSMA-11 PET/CT was done every 2-3 cycles or if disease progression was clinically suspected or based on change in PSA value (according to the PCWG3 criteria). Toxicity was measured using routine blood work up including blood counts, liver and renal function, and was graded according to CTCAE v5.0 criteria. Survival outcome was calculated based on the Kaplan-Meier method.

RESULTS

Further PSA decline of 33 ± 28% during the extended treatment was observed in 21/26 (81%) patients, whereas 5/26 (19%) patients showed a PSA increase; correspondingly in 11/21 patients with an initial response (PR or SD) to extended cycles, treatment was discontinued due to progressive disease, whereas six (23%) patients achieved low-volume residual disease. Two (8%) patients died without showing progression, and two (8%) patients are still under therapy. The median progression-free survival was 19 (95% CI: 15-23) months, and the overall survival was 29 (95% CI: 18-40) months. Grade ≥ 3 hematological toxicities occurred in 4/26 (15%) patients during treatment extension, and nephrotoxicity (grade ≥ 3) was observed in 1/26 (4%) patient during the follow-up.

CONCLUSION

Extended radioligand therapy is a feasible treatment option in patients with high-volume residual tumor after the completion of standard treatment with six cycles of [¹⁷⁷Lu]Lu-PSMA-617. Improved survival and the acceptable safety profile warrant further investigation of the concept of additional cycles in selected patients.

Lutetium-177-PSMA-617: A Vision of the Future

In the last decade, many life-prolonging therapeutic options have emerged for metastatic castration-resistant prostate cancer (mCRPC). The recent VISION trial is the first to demonstrate a survival benefit of Lutetium-177[¹⁷⁷Lu]Lu-PSMA-617 in post-chemotherapy mCRPC. This journal club reviews the VISION trial in the context of the earlier TheraP trial of [¹⁷⁷Lu]Lu-PSMA-617 in mCRPC post docetaxel and androgen pathway inhibition, to provide direction for the real-world application of [¹⁷⁷Lu]Lu-PSMA-617. Treatment in the control groups differed significantly between both trials and may have influenced outcomes: TheraP mandated cabazitaxel whereas VISION’s design could not allow it. In both trials, [¹⁷⁷Lu]Lu-PSMA-617 had a good safety profile, with common adverse events being fatigue, nausea, dry mouth, marrow suppression and diarrhea. Given its efficacy and favorable safety even in heavily pre-treated patients, [¹⁷⁷Lu]Lu-PSMA-617 provides hope to mCRPC patients and may be applied to earlier disease stages in future investigations.

177Lu-PSMA Therapy for Metastatic Castration-Resistant Prostate Cancer: A Mini-Review of State-of-the-Art

BACKGROUND

Prostate specific membrane antigen (PSMA) ligand labeled with Lutetium-177 (177Lu) is a promising therapeutic option for metastatic castration-resistant prostate cancer (mCRPC). Several prospective and retrospective studies as well as clinical trials are completed or underway. This has ultimately led to the approval of this therapy by the US Food and Drug Administration (FDA) on March 23 2022. Our work aims to present a mini-review of the most recent research performed and the potential future directions of 177Lu-PSMA-radioligand therapy (RLT) for mCRPC patients.

MAIN BODY

For patients with mCRPCwho have met the eligibility criteria for 177Lu-PSMA RLT, numerous studies and trials are either ongoing or have been completed. The studies included in this review have reported overall biochemical response, defined as a prostate-specific antigen (PSA) decline of at least 50%, in at least 44% of patients with mCRPC. The median ranges of overall survival (OS) and radiographic progression-free survival (rPFS) were reported within 10.7-56 and 3.6-16 months, respectively. With data from several retrospective and prospective studies published, the safety of 177Lu-PSMA RLT in mCRPC has been confirmed and demonstrated by its low toxicity profile. Various studies have published pharmacokinetic/pharmacodynamic models to better understand the absorption, distribution, metabolism, and excretion of the RLT in this patient population. Findings have been published for 177Lu-PSMA RLT alone and in combination with other agents. We summarize their findings in our review.

CONCLUSIONS

The efficacy of 177Lu-PSMA RLT for patients with mCRPC has been proven thus far with promising results: PSA response, OS and rPFS when used alone or in combination with other treatment options, relative to the standard treatment options alone. The low toxicity profile noted also proves the safety of 177Lu-PSMA RLT in these patients.

Lutetium Lu 177 vipivotide tetraxetan for metastatic castration-resistant prostate cancer

INTRODUCTION

¹⁷⁷Lu-vipivotide tetraxetan is a radiopharmaceutical that selectively targets prostate-specific membrane antigen (PSMA) and delivers beta-radiations to kill prostate cancer cells.

AREAS COVERED

Extensive experience outside the United States as well as randomized phase II and phase III data demonstrate that ¹⁷⁷Lu-vipivotide tetraxetan is a safe, generally well tolerated, and effective therapy for men with mCRPC. ¹⁷⁷Lu-vipivotide tetraxetan was approved by the FDA in March 2022 for the treatment of PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) after androgen receptor pathway inhibition and taxane-based chemotherapy based on the results of the VISION trial.

EXPERT OPINION

This review discusses the development and studies leading to the approval of ¹⁷⁷Lu-vipivotide tetraxetan. In all, ¹⁷⁷Lu-vipivotide tetraxetan is an exciting new tool in the arsenal for men with mCRPC after novel androgen pathway inhibitors and at least one taxane chemotherapy. Optimal selection of patients, sequencing of ¹⁷⁷Lu-vipivotide tetraxetan with the other agents available to treat mCRPC, and the use of dosimetry are current areas of interest with great potential and opportunities for further individual patient optimization using the tools of theranostics.

Management of Patients with Advanced Prostate Cancer: Report from the Advanced Prostate Cancer Consensus Conference 2021

BACKGROUND

Innovations in treatments, imaging, and molecular characterisation in advanced prostate cancer have improved outcomes, but various areas of management still lack high-level evidence to inform clinical practice. The 2021 Advanced Prostate Cancer Consensus Conference (APCCC) addressed some of these questions to supplement guidelines that are based on level 1 evidence.

OBJECTIVE

To present the voting results from APCCC 2021.

DESIGN, SETTING, AND PARTICIPANTS

The experts identified three major areas of controversy related to management of advanced prostate cancer: newly diagnosed metastatic hormone-sensitive prostate cancer (mHSPC), the use of prostate-specific membrane antigen ligands in diagnostics and therapy, and molecular characterisation of tissue and blood. A panel of 86 international prostate cancer experts developed the programme and the consensus questions.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The panel voted publicly but anonymously on 107 pre-defined questions, which were developed by both voting and non-voting panel members prior to the conference following a modified Delphi process.

RESULTS AND LIMITATIONS

The voting reflected the opinions of panellists and did not incorporate a standard literature review or formal meta-analysis. The answer options for the consensus questions received varying degrees of support from panellists, as reflected in this article and the detailed voting results reported in the Supplementary material.

CONCLUSIONS

These voting results from a panel of experts in advanced prostate cancer can help clinicians and patients to navigate controversial areas of management for which high-level evidence is scant. However, diagnostic and treatment decisions should always be individualised according to patient characteristics, such as the extent and location of disease, prior treatment(s), comorbidities, patient preferences, and treatment recommendations, and should also incorporate current and emerging clinical evidence and logistic and economic constraints. Enrolment in clinical trials should be strongly encouraged. Importantly, APCCC 2021 once again identified salient questions that merit evaluation in specifically designed trials.

PATIENT SUMMARY

The Advanced Prostate Cancer Consensus Conference is a forum for discussing current diagnosis and treatment options for patients with advanced prostate cancer. An expert panel votes on predefined questions focused on the most clinically relevant areas for treatment of advanced prostate cancer for which there are gaps in knowledge. The voting results provide a practical guide to help clinicians in discussing treatment options with patients as part of shared decision-making.

Hematological Toxicity in Mice after High Activity Injections of 177Lu-PSMA-617

Prostate cancer (PC) is one of the most common malignancies affecting men, with poor prognosis after progression to metastatic castration-resistant prostate cancer (mCRPC). Radioligand therapy (RLT) targeting the overexpressed PSMA on PC cells, with, e.g., ¹⁷⁷Lu-PSMA-617, has been effective in reducing tumor burden and prolonging survival in mCRPC. However, it is not a curative method with kidney and bone marrow toxicity limiting the activity given to patients. Previous preclinical models have reported transient hematotoxicity for up to 120 MBq. This activity may still be too low to investigate the effect on renal function since it corresponds to an absorbed dose below 10 Gy, whereas the kidneys in a clinical setting usually receive an absorbed dose more than double. Here we investigated the hematotoxicity and recovery after administered activities of 120, 160, and 200 MBq in a ¹⁷⁷Lu-PSMA-617 BALB/cAnNRj mouse model. The animals had an initial drop in white blood cells (WBC) starting 4 days post injection, which recovered after 21 days. The effect on red blood cells (RBC) and platelets was detected later; 17 days post-injection levels decreased compared to the control group. The reduction was restored again 32 days post injection. No correlation between injected activity and hematotoxicity was found. Our results suggest that activities up to 200 MBq of ¹⁷⁷Lu-PSMA-617 give transient hematotoxicity from which animals recover within a month and no radiation-related deaths. Injecting these high activities could allow animal studies with increased clinical relevance when studying renal toxicity in animal models.

Hematotoxicity and Nephrotoxicity in Prostate Cancer Patients Undergoing Radioligand Therapy with [177Lu]Lu-PSMA I&T

Simple Summary

Radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-directed agents has shown remarkable results in patients with advanced prostate cancer. Our objective was to provide data on the side effect profile of PSMA-directed RLT using the therapeutic radiotracer [¹⁷⁷Lu]Lu-PSMA I&T. We evaluated patients with castration-resistant metastatic prostate cancer treated with at least three cycles of [¹⁷⁷Lu]Lu-PSMA I&T. A substantial fraction of the patients already had impaired renal function and/or reduced white blood cell counts at baseline, but the degree of nephrotoxicity or hematotoxicity under RLT was low. No severe toxicities occurred under RLT.

Abstract

(1) Background: Prostate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) has shown remarkable results in patients with advanced prostate cancer. We aimed to evaluate the toxicity profile of the PSMA ligand [¹⁷⁷Lu]Lu-PSMA I&T. (2) Methods: 49 patients with metastatic, castration-resistant prostate cancer treated with at least three cycles of [¹⁷⁷Lu]Lu-PSMA I&T were evaluated. Prior to and after RLT, we compared leukocytes, hemoglobin, platelet counts, and renal functional parameters (creatinine, eGFR, n = 49; [^99mTc]-MAG3-derived tubular extraction rate (TER), n = 42). Adverse events were classified according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0 and KDIGO Society. To identify predictive factors, we used Spearman’s rank correlation coefficient. (3) Results: A substantial fraction of the patients already showed impaired renal function and reduced leukocyte counts at baseline. Under RLT, 11/49 (22%) patients presented with nephrotoxicity CTCAE I or II according to creatinine, but 33/49 (67%) according to eGFR. Only 5/42 (13%) showed reduced TER, defined as <70% of the age-adjusted mean normal values. Of all renal functional parameters, absolute changes of only 2% were recorded. CTCAE-based re-categorization was infrequent, with creatinine worsening from I to II in 2/49 (4.1%; GFR, 1/49 (2%)). Similar results were recorded for KDIGO (G2 to G3a, 1/49 (2%); G3a to G3b, 2/49 (4.1%)). After three cycles, follow-up eGFR correlated negatively with age (r = −0.40, p = 0.005) and the eGFR change with Gleason score (r = −0.35, p < 0.05) at baseline. Leukocytopenia CTCAE II occurred only in 1/49 (2%) (CTCAE I, 20/49 (41%)) and CTCAE I thrombocytopenia in 7/49 (14%), with an absolute decrease of 15.2% and 16.6% for leukocyte and platelet counts. Anemia CTCAE II occurred in 10/49 (20%) (CTCAE I, 36/49 (73%)) with a decrease in hemoglobin of 4.7%. (4) Conclusions: After PSMA-targeted therapy using [¹⁷⁷Lu]Lu-PSMA I&T, no severe (CTCAE III/IV) toxicities occurred, thereby demonstrating that serious adverse renal or hematological events are unlikely to be a frequent phenomenon with this agent.

Safety and Efficacy of 177Lutetium-PSMA-617 Radioligand Therapy Shortly after Failing 223Radium-Dichloride

Bone-seeking 223Radium-dichloride (223Ra) is an established treatment prolonging survival and reducing morbidity in selected patients with metastatic castration-resistant prostate cancer (mCRPC) with skeletal involvement. Radioligand therapy with 177Lutetium-PSMA-617 (177Lu-PSMA-617) has been increasingly implemented in patients with mCRPC failing conventional treatment options. In this study, the safety and efficacy of 177Lu-PSMA-617 in patients with progressive bone involvement under treatment with 223Ra was assessed. Twenty-eight men (median age 73 years, range 63–89 years) with progressive mCRPC, who started 177Lu-PSMA-617 within 8 weeks after the last 223Ra administration, received a median of 4 (IQR 3–6) and a total of 120 cycles of 223Ra and a median of 4 (IQR 2–7) cycles 177Lu-PSMA-617 with a mean treatment activity of 6.5 ± 1.2 GBq per cycle, reaching a mean cumulative activity of 30.7 ± 23.4 GBq. A PSA response (≥50% PSA decline 12 weeks after the first 177Lu-PSMA-617 cycle) was observed in 18/28 (64.3%) patients and imaging-based partial remission (PR) was observed in 11/28 (39.3%) patients. Median imaging-based progression-free survival (PFS) was 10 (95% CI, 6–14) months and median overall survival (OS) was 18 (95% CI, 14–22) months. Patients with low bone tumor burden (2–20 lesions) had a significantly longer OS (28 vs. 14 months, p < 0.045) compared to patients with a high tumor burden (>20 lesions). Grade ≥ 3 hematological toxicity was observed in six patients after their last treatment cycle with anemia, leukopenia and thrombocytopenia in 5/28 (17.9%), 4/28 (14.3%) and 6/28 (21.4%) patients, respectively. In progressive bone-metastatic mCRPC patients, prompt initiation of 177Lu-PSMA-617 after failing 223Ra is effective with an acceptable toxicity profile.