Prostate-specific membrane antigen as a possible target for radionuclide treatment of adenoid cystic carcinoma

Abstract

Background: Adenoid cystic carcinoma (AdCC) is an uncommon malignant epithelial tumour of secretory glands. Many patients develop slow-growing local recurrences and/or distant metastasis within ten years, which are responsible for most long-term morbidity and mortality. Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein of prostate epithelial cells, was originally described as highly prostate-specific. However, radionuclide imaging using Gallium-68-labelled PSMA and positron emission tomography (PET)/computed tomography (CT) showed tracer uptake in several other organs and types of malignancies. Objective: We present the results of 68Ga-PSMA-PET/CT imaging and immunohistochemical PSMA expression in patients with AdCC. Methods: Eight patients with known or suspected local recurrent and/or distant metastatic AdCC underwent full-body 68Ga-PSMA-11-PET/CT. Standardised uptake values (SUVmax) were calculated of the regions of recurrent tumour and distant metastasis. Tumour specimens were revised from the pathology archives and immunohistochemically stained for PSMA expression. Results: Four patients developed local recurrence, all suffered distant metastasis. 7/8 (88%) of the patients depicted PSMA-positive AdCC on PSMA-PET/CT. In these seven positive PET/CTs, mean SUVmax was 6.2 for local recurrence and 5.5 for distant metastasis. 6/8 (75%) of primary resection specimens were positive on PSMA immunohistochemistry. All available specimens of local recurrent and distant metastatic AdCC showed PSMA expression. Conclusions: 68Ga-PSMA-PET/CT imaging is a promising and possibly better imaging modality in staging and follow-up of AdCC. Until now, curative treatment of deep recurrences or metastatic AdCC is often impossible. Due to high PSMA expression of many of these tumours, AdCC might be candidate for targeted anti-tumour treatment with the beta-emitter Lutetium-177-PSMA-617.