Receptor targeted imaging using prostate specific membrane antigen (PSMA)-a labeled radioisotope currently plays a key role in prostate cancer imaging. This is due to the overexpression of PSMA, a type II Tran's membrane protein, in prostate cancer cells. Gallium-68 and fluorine-18 labeled PSMA are currently available for positron emission tomography/ computed tomography (PET/CT) imaging for the diagnosis, staging, treatment planning and follow-up of prostate cancer.
In this case report we discuss a 70 year old male who presented with progressively rising serum prostate-specific antigen (PSA) levels. Three prostate biopsies performed at different time points were negative and failed to provide a histological diagnosis. 68Ga-PSMA PET/CT was subsequently requested to guide biopsy and appropriately stage the disease. PSA level at the time of imaging was 39ng/ml. Uptake was demonstrated in the left posterior-lateral aspect of the prostate gland (SUVmax=15.27), identifying the target biopsy site for histological confirmation of the diagnosis of prostate cancer (Figure 1).
Unusual uptake was also noted in a right axillary lymph node (SUVmax=6.18). Biopsy of this lymph node confirmed Hodgkin's Lymphoma (Figure 2&3).This clinical case demonstrates the non-specific nature of PSMA in prostate cancer, despite its name. We would like to advise caution in the interpretation of distant nodal uptake sites on 68Ga-PSMA PET/CT imaging for the diagnosis and/or staging of prostate cancer.