A prospective study of 68Ga-PSMA PET/CT imaging of HCC as diagnosed on conventional imaging to evaluate for potential 177Lu-PSMA therapy

Prostate-specific membrane antigen-targeting radiopharmaceuticals: a new frontier in hepatic malignancies

Background/Objectives

Prostate-specific membrane antigen (PSMA) is overexpressed in prostate hypercellularity, making it an effective target for molecular imaging and therapy of prostate cancer. PSMA is expressed in the neovasculature of hepatic malignancies and regulates tumor cell invasion and angiogenesis. The diagnosis and treatment of hepatic malignancies remain challenging. Thus, radiopharmaceuticals targeting PSMA are gaining prominence in the treatment of hepatic malignancies. Therefore, this review aims to discuss the applications of PSMA-targeting radiopharmaceuticals in hepatic malignant tumors, focusing on hepatocellular carcinoma (HCC), to assess their value as a diagnostic and therapeutic agent for hepatic malignancies.

Methods

The potentials of PSMA-targeting radiopharmaceuticals for diagnostic and therapeutic use in hepatic malignancies were investigated. Moreover, their characteristics, diagnostic and therapeutic efficacies, and potential synergies when used in conjunction with other therapeutic modalities were elucidated.

Results

Computed tomography (CT) and magnetic resonance imaging (MRI) are the most common imaging modalities in clinical practice; however, their sensitivity is not optimal. PSMA positron emission tomography/CT can be used as a complementary modality to conventional imaging for characterizing lesions, staging and/or re-staging HCC, and assessing treatment response when conventional imaging results are unclear. Moreover, most patients with HCC are diagnosed at an advanced stage in which treatment options are limited. Hence, PSMA-based radioligand therapy serves as a promising alternative treatment when multiple treatments fail.

Conclusions

Further research and clinical transformation are required to effectively diagnose and treat HCC via PSMA targeting. This will have significant clinical application prospects in primary and secondary hepatic malignancies.

[68Ga]Ga-PSMA-617 PET/MRI for imaging patients suspected of hepatocellular carcinoma

PURPOSE

Radiolabeled probes targeting prostate-specific membrane antigen (PSMA) have been used in prostate cancer. Moreover, PSMA is also overexpressed on neovessels in hepatocellular carcinoma (HCC). This study aimed to preliminarily evaluate the diagnostic effectiveness of [68Ga]Ga-PSMA-617 PET/MRI for HCC.

METHODS

Patients suspected of HCC were prospectively enrolled in this single-center study (NCT05006326, 2021-08-16) to perform [68Ga]Ga-PSMA-617 PET/MRI, along with contrast enhanced CT (ceCT) or ceMRI. The main suspicious intrahepatic lesions were resected and pathologically verified. Visual evaluation of [68Ga]Ga-PSMA-617 PET/MRI images was performed on all lesions. Maximum standard uptake value (SUVmax), mean standard uptake value (SUVmean), tumor-to-liver ratio (TLR), tumor-to-blood ratio (TBR), and tumor-to-parotid ratio (TPR) were measured or calculated. The diagnostic efficiency of different modalities was summarized. PSMA expression was evaluated by immunohistochemistry and the correlation of PSMA expression and [68Ga]Ga-PSMA-617 uptake in HCC primary tumors was quantitatively analyzed.

RESULTS

A total of 12 patients (ten men and two women; mean age 58.75 ± 12.08 years) were included. Ten patients were diagnosed with HCC, 2 with intrahepatic cholangiocarcinoma (ICC), and 4 with hemangioma. The SUVmax, TLR, TBR, and TPR of HCC primary tumors were higher than those of ICC and hemangioma. The diagnostic accuracy of [68Ga]Ga-PSMA-617 PET/MRI for primary HCC was 82.4%. When combined with ceCT or ceMRI, the accuracy increased to 88.2%. A moderate correlation was observed between SUVmax and mean PSMA expression in HCC primary tumors (R = 0.788).

CONCLUSION

Utilizing a hybrid PET/MRI system to combine [68Ga]Ga-PSMA-617 PET/MRI with ceMRI is a promising one-stop solution for the accurate diagnosis of HCC.

TRIAL REGISTRATION

NCT05006326. Registered August 16, 2021, https://clinicaltrials.gov/study/NCT05006326 .

Targeted radionuclide therapy for patients with central nervous system metastasis: Overlooked potential?

Targeted radionuclide therapy is an emerging therapeutic concept for metastatic cancer that can be considered if a tumor can be delineated by nuclear medicine imaging and also targeted based on the expression of a particular target (thera-nostics). This mode of treatment can also compete with or supplement conventional radiotherapy, for example, if MRI does not fully capture the extent of the disease, including microscopic metastases. Targeted radionuclide therapy for patients with thyroid cancer, with certain somatostatin receptor 2-expressing tumors and with prostate-specific membrane antigen-expressing prostate cancer is approved, and numerous approaches of targeted radionuclide therapy for patients with metastatic cancer are in development (eg, using fibroblast activation protein as a target). Although brain metastases are rare in cancers with approved targeted radionuclide therapies, there is no a priori reason to assume that such treatments would not be effective against brain metastases if the targets are expressed and not shielded by the blood-brain barrier. Here, we discuss the current state of the art and opportunities of targeted radionuclide therapies for patients with brain and leptomeningeal metastases.

Prostate-Specific Membrane Antigen (PSMA) PET/CT in the Detection and Diagnosis of Hepatocellular Carcinoma (HCC): A Systematic Review and Meta-Analysis

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) is widely used in prostate cancer. Recent studies indicate hepatocellular carcinoma (HCC) demonstrates PSMA PET uptake. The diagnostic accuracy of PSMA PET for HCC is not known. We conducted a systematic review and meta-analysis of studies assessing 68Ga-PSMA-11 in HCC. Nine studies were included, with 196 patients and a total of 491 HCC lesions. Per-patient analysis yielded a pooled sensitivity of 89.8% (95% CI 78.5-95.5). Specificity was poorly reported, with insufficient data. When per-lesion level analysis was performed on seven studies, the pooled sensitivity was 94.5% (95% CI 82.9-98.4), and specificity was again poorly reported with insufficient data. Among the three studies with adequate data for full per-lesion meta-analysis, 115 lesions in 41 patients demonstrated sensitivity of 97.1% (95% CI 87.8-99.4), while specificity was 42.2% (95% CI 0.3-99.4). Two studies provided sufficient data for meta-analysis on a per-patient level (n = 50 patients), demonstrating a sensitivity of 92.5% (95% CI 64.0-98.9) and specificity of 72.4% (95% CI 1.3-99.8). PSMA PET demonstrates a high sensitivity for HCC and shows promise as an imaging modality for diagnosis and staging of HCC. However, the existing literature does not provide enough data to confidently evaluate its specificity and, therefore, accuracy. Further prospective studies are necessary, with a focus on the accurate reporting of benign lesions and inclusion of patients with an intermediate probability of HCC.

Radionuclide Therapy With 177 Lu-PSMA in a Patient With Hepatocellular Carcinoma

ABSTRACT

A 69-year-old man diagnosed with progressive bone metastatic castration-resistant prostate adenocarcinoma and concurrent alcoholic cirrhosis with multiple hepatocellular carcinoma (HCC) nodules was referred to our nuclear medicine service for 177 Lu-PSMA-617 therapy. The patient's pretreatment screening using 68 Ga-PSMA-11 PET/CT revealed high prostate-specific membrane antigen expression in both prostatic and HCC lesions. The patient underwent 2 doses of 177 Lu-PSMA-617. Subsequent imaging assessments with 68 Ga-PSMA-11 PET/CT and hepatic MRI indicated progressive HCC nodules, while showing a partial response in prostatic bone metastases. Positive clinical and biological responses were observed only in prostatic disease, but not in HCC nodules.