68Gallium-Prostate-Specific Membrane Antigen PET/Computed Tomography for Primary and Secondary Staging in Prostate Cancer

Detection and localisation of primary prostate cancer using 68 gallium prostate-specific membrane antigen positron emission tomography/computed tomography compared with multiparametric magnetic resonance imaging and radical prostatectomy specimen pathology

OBJECTIVE

To compare the accuracy of ⁶⁸ gallium prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸ Ga-PSMA PET/CT) with multiparametric MRI (mpMRI) in detecting and localising primary prostate cancer when compared with radical prostatectomy (RP) specimen pathology.

PATIENTS AND METHODS

Retrospective review of men who underwent ⁶⁸ Ga-PSMA PET/CT and mpMRI for primary prostate cancer before RP across four centres between 2015 and 2018. Patients undergoing imaging for recurrent disease or before non-surgical treatment were excluded. We defined pathological index tumour as the lesion with highest International Society of Urological Pathology Grade Group (GG) on RP specimen pathology. Our primary outcomes were rates of accurate detection and localisation of RP specimen pathology index tumour using ⁶⁸ Ga-PSMA PET/CT or mpMRI. We defined tumour detection as imaging lesion corresponding with RP specimen tumour on any imaging plane, and localisation as imaging lesion matching RP specimen index tumour in all sagittal, axial, and coronal planes. Secondary outcomes included localisation of clinically significant and transition zone (TZ) index tumours. We defined clinically significant disease as GG 3-5. We used descriptive statistics and the Mann-Whitney U-test to define and compare demographic and pathological characteristics between detected, missed and localised tumours using either imaging modality. We used the McNemar test to compare detection and localisation rates using ⁶⁸ Ga-PSMA PET/CT and mpMRI.

RESULTS

In all, 205 men were included in our analysis, including 133 with clinically significant disease. There was no significant difference between ⁶⁸ Ga-PSMA PET/CT and mpMRI in the detection of any tumour (94% vs 95%, P > 0.9). There was also no significant difference between localisation of all index tumours (91% vs 89%, P = 0.47), clinically significant index tumours (96% vs 91%, P = 0.15) or TZ tumours (85% vs 80%, P > 0.9) using ⁶⁸ Ga-PSMA PET/CT and mpMRI. Limitations include retrospective study design and non-central review of imaging and pathology.

CONCLUSION

We found no significant difference in the detection or localisation of primary prostate cancer between ⁶⁸ Ga-PSMA PET/CT and mpMRI. Further prospective studies are required to evaluate a combined PET/MRI model in minimising tumours missed by either modality.

Advances in prostate-specific membrane antigen PET of prostate cancer

PURPOSE OF REVIEW

In recent years, a large number of reports have been published on prostate-specific membrane antigen (PSMA)/PET in prostate cancer (PCa). This review highlights advances in PSMA PET in PCa during the past year.

RECENT FINDINGS

PSMA PET/computed tomography (CT) is useful in detection of biochemical recurrence, especially at low prostate-specific antigen (PSA) values. The detection rate of PSMA PET is influenced by PSA level. For primary PCa, PSMA PET/CT shows promise for tumour localization in the prostate, especially in combination with multiparametric MRI (mpMRI). For primary staging, PSMA PET/CT can be used in intermediate and high-risk PCa. Intraoperative PSMA radioligand guidance seems promising for detection of malignant lymph nodes. While the use of PSMA PET/MRI in primary localized disease is limited to high and intermediate-risk patients and localized staging, in the recurrence setting, PET/MRI can be particularly helpful when the lesions are subtle. PSMA PET/CT is superior to choline PET/CT and other conventional imaging modalities.

SUMMARY

Molecular imaging with PSMA PET continues to pave the way for personalized medicine in PCa.However, large prospective clinical studies are still needed to fully evaluate the role of PSMA PET/CT and PET/MRI in the clinical workflow of PCa.

Clinical perspectives of PSMA PET/MRI for prostate cancer

Prostate cancer imaging has become an important diagnostic modality for tumor evaluation. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) has been extensively studied, and the results are robust and promising. The advent of the PET/magnetic resonance imaging (MRI) has added morphofunctional information from the standard of reference MRI to highly accurate molecular information from PET. Different PSMA ligands have been used for this purpose including 68gallium and 18fluorine-labeled PET probes, which have particular features including spatial resolution, imaging quality and tracer biodistribution. The use of PSMA PET imaging is well established for evaluating biochemical recurrence, even at low prostate-specific antigen (PSA) levels, but has also shown interesting applications for tumor detection, primary staging, assessment of therapeutic responses and treatment planning. This review will outline the potential role of PSMA PET/MRI for the clinical assessment of PCa.