Prostate-Specific Membrane Antigen Ligands for Imaging and Therapy

Intraindividual Comparison of 18F-PSMA-1007 and 18F-DCFPyL PET/CT in the Prospective Evaluation of Patients with Newly Diagnosed Prostate Carcinoma: A Pilot Study

The introduction of ¹⁸F-labeled prostate-specific membrane antigen (PSMA)-targeted PET/CT tracers, first ¹⁸F-DCFPyL (2-(3-{1-carboxy-5-[(6-¹⁸F-fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid) and more recently ¹⁸F-PSMA-1007 (((3S,10S,14S)-1-(4-(((S)-4-carboxy-2-((S)-4-carboxy-2-(6-¹⁸F-fluoronicotinamido)butanamido)butanamido)methyl)phenyl)-3-(naphthalen-2-ylmethyl)-1,4,12-trioxo-2,5,11,13-tetraazahexadecane-10,14,16-tricarboxylic acid)), have demonstrated promising results for the diagnostic workup of prostate cancer. This clinical study presents an intraindividual comparison to evaluate tracer-specific characteristics of ¹⁸F-DCFPyL versus ¹⁸F-PSMA-1007. Methods: Twelve prostate cancer patients, drug-naïve or before surgery, received similar activities of about 250 MBq of ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007 48 h apart and were imaged 2 h after injection on the same PET/CT scanner using the same reconstruction algorithm. Normal-organ biodistribution and tumor uptake were quantified using SUV_maxResults: PSMA-positive lesions were detected in 12 of 12 prostate cancer patients. Both tracers, ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007, detected the same lesions. No statistical significance could be observed when comparing the SUV_max of ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007 for local tumor, lymph node metastases, and bone metastases. With regard to normal organs, ¹⁸F-DCFPyL had statistically significant higher uptake in kidneys, urinary bladder, and lacrimal gland. Vice versa, significantly higher uptake of ¹⁸F-PSMA-1007 in muscle, submandibular and sublingual gland, spleen, pancreas, liver, and gallbladder was observed. Conclusion: Excellent imaging quality was achieved with both ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007, resulting in identical clinical findings for the evaluated routine situations. Nonurinary excretion of ¹⁸F-PSMA-1007 might present some advantage with regard to delineation of local recurrence or pelvic lymph node metastasis in selected patients; the lower hepatic background might favor ¹⁸F-DCFPyL in late stages, when rare cases of liver metastases can occur.

Diagnostic performance of 68Gallium-PSMA-11 PET/CT to detect significant prostate cancer and comparison with 18FEC PET/CT

Background

Radiolabeled prostate-specific membrane antigen (PSMA) has proven to be a highly accurate method to detect recurrence and metastases of prostate cancer, but only sparse data is available about its performance in the diagnosis of clinically significant primary prostate cancer.

Methods

We compared ⁶⁸Ga-PSMA-11 PET/CT in 25 patients with ¹⁸FEC PET/CT in 40 patients with suspected prostate carcinoma based on an increased PSA level.The PET/CT results were compared with the histopathologic Gleason Score (GS) of biopsies.

Results

The ⁶⁸Ga-PSMA-11 PET/CT revealed highly suspect prostatic lesions (maximum standardized uptake value/SUV_max >2.5) in 21/25 patients (84%), associated with GS≥6 (low-grade/high-grade carcinoma). Two histopathologic non-malignancy-relevant cases (GS<6) had PSMA-SUV_max ≤2.5; all histopathologic high-grade cases (GS≥7b) showed PSMA-SUV_max >12.0 which further increased with rising GS. There were 2 false positives and no false negative findings for high-grade prostate cancer using a cut off-level for SUV_max of 2.5.In contrast, the ¹⁸FEC PET/CT showed suspected malignant lesions in 38/40 patients (95%), which included 3 lesions with GS<6. The mean SUV_max values did not differ with different GS. There were 11 false positives and 1 false negative for detection of high-grade prostate cancer (cut off 2.5).By means of ROC analysis a SUV_max of 5.4 was found to be an optimal cut off-level to distinguish between low- and high-grade carcinoma in ⁶⁸Ga-PSMA-11 PET/CT (AUC=0.9692; 95% CI 0.9086;1.0000;SD(AUC)=0.0309)). Choosing a cut off-level of SUV_max5.4, ⁶⁸Ga-PSMA-11 PET/CT was able to distinguish between GS ≤7a/≥7b with a sensitivity of 84%, a specificity of 100%, a negative predictive value (NPV) of 67%, and an efficiency of 88% (p<0.001).The ROC analysis revealed a SUV_max 6.5 as an optimal cut off-level to distinguish between low- and high-grade carcinoma in ¹⁸FEC PET/CT (AUC=0.7470; 95% CI 0.5919;0.9020;SD(AUC)=0.0791) with a sensitivity of 61% and a specificity of 92%; but the efficiency was only 70% and the NPV 50% (p=0.01).

Conclusion

⁶⁸Ga-PSMA-11 PET/CT guided biopsy of the prostate increases diagnostic precision and is likely to help to reduce overtreatment of low-grade malignant disease as well as detect the foci of the highest Gleason pattern. Both methods (⁶⁸Ga-PSMA-11,¹⁸FEC) were suitable to detect primary prostate cancer, but the excellent image quality, the higher specificity and the good correlation of positive scans with GS are advantages of ⁶⁸Ga-PSMA-11.