68Ga]Gallium-labelled PSMA ligand as superior PET tracer for the diagnosis of prostate cancer: comparison with 18F-FECH

Abstract

Prostate-specific membrane antigen (PSMA) is a cell surface protein, which is expressed at higher levels in prostate cancer compared to other tissues. This protein provides a promising target for specific imaging and therapy due to its transmembrane location and internalization after ligand binding [1]. PSMA is also expressed in the neovasculature of many solid tumours [2, 3]. Recently procedures have been developed to label PSMA with Ga and I for positron emission tomography (PET) imaging [4, 5]. We present for the first time PET/CT images obtained with Ga-labelled HBED-CC conjugate of the PSMA-specific pharmacophore Glu-NH-CO-NH-Lys (Ga-PSMA). The images were compared with [F]FECH PET/CT of the same patient. The 67-year-old patient had undergone previous radiotherapy of the prostate due to carcinoma and had received androgen therapy since 2002. The patient presented with a continuous increase of PSA values (from 1 ng/ml in 2002 to 7.4 ng/ml in May 2011) and was referred to our department for further analysis using PET/CT. F-FECH PET/CT was unable to detect any lesions. However, Ga-PSMA PET/CT did show a lesion adjacent to the urinary bladder compatible with tumour relapse (figure). Our initial experience with Ga-PSMA PET/CT strongly suggests that this novel method can detect prostate carcinoma relapses and metastases with significantly improved contrast compared to F-FECH PET/CT. Further clinical studies should confirm this observation and determine if PSMA PET/CT can replace F-FECH PET/CT in the diagnosis of prostate carcinoma.