<sup>68</sup>Ga-PSMA-HBED-CC PET/CT imaging for adenoid cystic carcinoma and salivary duct carcinoma: a phase 2 imaging study
Wim van Boxtel, Susanne Lütje, Ilse C.H. van Engen-van Grunsven, Gerald W. Verhaegh, Jack A. Schalken, Marianne A. Jonker, James Nagarajah, Martin Gotthardt, Carla M.L. van Herpen
Abstract
Rationale: Treatment options for recurrent and/or metastatic (R/M) adenoid cystic carcinoma (ACC) and salivary duct carcinoma (SDC), major subtypes of salivary gland cancer, are limited. Both tumors often show overexpression of prostate-specific membrane antigen (PSMA). In prostate cancer, PSMA-ligands labeled with 68 Ga or 177 Lu are used for imaging and therapy, respectively. Primary aim of this study in R/M ACC and SDC patients was to systematically investigate 68 Ga-PSMA-uptake by PET/CT imaging to determine if PSMA radionuclide therapy could be a treatment option. Methods: In a prospective phase II study, PET/CT imaging was performed 1 h post injection of 68 Ga-PSMA-HBED-CC in 15 ACC patients and 10 SDC patients. Maximum standardized uptake values (SUV) were determined in tumor lesions. Immunohistochemical PSMA expression was scored in primary tumors and metastatic tissue. Standard imaging (MRI or CT) was performed for comparison. Results: In ACC patients, SUVmax ranged from 1.1 to 30.2 with a tumor/liver-ratio >1 in 13 out of 14 evaluable patients (93%). In SDC patients, SUVmax ranged from 0.3 to 25.9 with a tumor/liver-ratio >1 in 4 out of 10 patients (40%). We found a large intra-patient inter-metastatic variation in uptake of 68 Ga-PSMA, and immunohistochemistry did not predict ligand uptake in ACC and SDC. Finally, PSMA-PET detected additional bone metastases compared to CT in 2 ACC patients with unexplained pain.