1342P - 68Ga-PSMA-PET/CT imaging for locally advanced, recurrent and metastatic adenoid cystic carcinoma and salivary duct carcinoma

Abstract

Background: Salivary gland cancer (SGC) is a rare cancer with few treatment options. Adenoid cystic carcinoma (ACC) and salivary duct carcinoma (SDC) are major subtypes of SGC which often show immunohistochemical expression of prostate-specific membrane antigen (PSMA). In prostate cancer, PSMA ligands labeled with radioisotopes such as 68Ga or 177Lu, are used for imaging or therapy. The aim of this study was to evaluate 68Ga-PSMA ligand uptake in patients with locally recurrent and/or metastatic ACC and SDC and to establish the diagnostic value of 68Ga-PSMA-PET/CT imaging compared to full-dose CT imaging. Methods:68Ga-PSMA-HBED-CC PET/CT scans were performed in 14 ACC patients and 10 SDC patients including a full-dose CT scan of the neck, chest and abdomen. 68Ga-PSMA ligand uptake was evaluated in local recurrences and metastatic lesions. Detected lesions were compared to CT results. Maximum standardized uptake values (SUVmax) were determined. The study protocol was approved by the local medical ethical committee and a written informed consent was obtained from all patients. Results: Moderate to intense PSMA ligand uptake was observed in local recurrences and distant metastases in all ACC patients and 40% of SDC patients. In addition, PSMA-PET imaging detected additional bone metastases in 2 ACC patients and additional lymph node metastases in 1 ACC patient which were not detected on a full-dose CT scan. In 1 ACC patient a local recurrence of a vulvar ACC was suspected on CT but PSMA-PET imaging was negative, which turned out to be scar tissue, eventually. Conclusions: PSMA-PET imaging showed moderate to intense ligand uptake in local recurrences and distant metastases of all ACC patients and 40% of SDC patients. Based on the high uptake, these patients may be promising candidates for 177Lu-PSMA radioligand therapy in future. Moreover, PSMA-PET imaging has added diagnostic value compared to full-dose CT imaging. Clinical trial identification: NCT03319641. Legal entity responsible for the study: Radboud university medical center, Nijmegen, the Netherlands. Funding: Adenoid Cystic Carcinoma Research Foundation (ACCRF) and the Dutch Salivary Gland Cancer Patient Platform. Disclosure: All authors have declared no conflicts of interest.