Biodistribution/Reproducibility Ga-68 PSMA-HBED-CC

Prostate cancer (PCa) represents the most common noncutaneous cancer and second most common cause of cancer related death among men in the United States and worldwide. Individual PCa tumor behavior is variable. Some tumors show slow indolent growth patterns and may never become clinically significant while others are aggressive and lead to metastases and death. PCa most commonly metastasizes to bone and lymph nodes. Lungs, liver, and adrenal glands are less frequent metastatic sites.

Accurate staging and risk stratification is essential to optimal management. Pelvic lymph node dissection (PLND) which is performed along with radical prostatectomy is the gold standard for detection of occult nodal metastases but is invasive and has associated morbidity. PLND offers an additional therapeutic benefit in some patients, but is also associated with potential complications and can still underestimate the extent of nodal metastases as 40-50% fall outside the traditional dissection zones [6]. Furthermore, fewer patients are presenting with nodal metastases at initial presentation due to stage migration, so more PLNDs need to be performed to benefit one patient. Therefore there is a clear need for noninvasive imaging options to assist with early and accurate detection of nodal metastases.

68Ga PSMA-HBED-CC is a urea-based small molecular inhibitor that targets an enzymatic site on the extracellular domain of the PSMA membrane protein. Based on strong preclinical evidence, a number of clinical studies of 68Ga PSMA-HBED-CC PET/CT have been performed. Afshar-Oromieh et al. showed detection of lesions suspicious for PCa metastases in 84% of a cohort of patients (n=37) being investigated for biochemical relapse, clarification of suspicious findings on other modalities, or evaluation for possible 131I PSMA ligands. In a larger retrospective study (n=319) Afshar-Oromieh et al. showed that 68Ga PSMA-HBED-CC PET/CT detected PCa in 83% of patients with suspected recurrence. In another study Afshar-Oromieh et al compared 68Ga PSMA-HBED-CC PET/CT to 18F fluoromethylcholine (FCH) PET/CT. At least one PCa lesion was detected in 87% of patients with 68Ga PSMA-HBED-CC versus 70% of patients with 18F FCH. Among patients in whom PSA values were <2.82 ng/ml at least one lesion could be detected in 69% of patients with 68Ga PSMA-HBED-CC and 44% patients with 18F FCH. Tumor-to-background ratios were higher for 68Ga PSMA-HBED-CC. In the aforementioned studies by Afshar-Oromieh et al. 49 patients with positive scans were further evaluated by biopsy or surgery and were confirmed as PCa with no false positives. Morigi et al. also showed the superiority of 68Ga PSMA-HBED-CC over 18F FCH in PET/CT. Detection rates 68Ga PSMA-HBED-CCPET/CT in multiple studies are higher than for rates reported in the literature for 11C Choline, 18F Choline, and 11C Acetate [20]. Most importantly the detection rates 68Ga PSMA-HBED-CCPET/CT in patients with low PSA (<0.5 ng/ml) are more favorable.

Thus preclinical and clinical studies show that 68Ga PSMA-HBED-CC PET/CT is a promising radiotracer for the early detection of metastatic or recurrent PCa even with low serum PSA levels.