Explorative study, which evaluates the effect of androgen deprivation therapy (ADT) on the PSMA ligand uptake on 68Ga-PSMA-PET/CT in salivary duct carcinoma patients.

Rationale: Prostate specific membrane antigen (PSMA) is a transmembrane protein, which is expressed on prostate cancers cells and other malignancies. Recently, several ligands have been developed that target PSMA. Linked to Gallium-68, this enables diagnostic 68Ga-PSMA-PET/CT scans. Linked to Lutetium-177 enables therapeutic 177Lu-PSMA Radioligand therapy. Most research on the diagnostic and therapeutic possibilities of PSMA has been conducted in patients with advanced prostate cancer.

This research group investigates whether these findings also apply to salivary gland cancer (SGC), a rare cancer. Previously the investigators conducted a phase II 68Ga-PSMA imaging study (NCT03319641), to evaluate PSMA ligand uptake in locally advanced, recurrent and metastatic ACC and SDC (two subtypes of SGC). A relevant PSMA-ligand uptake was observed in 93% of ACC patients and 40% of SDC patients. However, since 60% of SDC patients showed low ligand uptake, these patients are not suitable for PSMA radioligand therapy. For advanced SDC, androgen deprivation therapy is often given as first-line treatment, because the majority of SDCs are androgen receptor positive. In prostate cancer, androgen deprivation therapy (ADT) can increase PSMA-ligand uptake. Therefore the aim is to investigate if ADT can increase the uptake of 68Ga-PSMA in patients with R/M SDC, as has previously been demonstrated in prostate cancer.

Objective: The primary objective is to investigate if ADT can increase the uptake of 68Ga-PSMA in patients with R/M SDC.

Study design: Interventional clinical trial, an explorative study. Study population: Patients with locally advanced, recurrent or metastatic (R/M) SDC AR+ and who will start ADT as standard of care.

Inclusion Criteria:

• Patients must have the ability to provide written informed consent.
• Patients must be ≥ 18 years of age.
• Patients must have histological, pathological, and/or cytological confirmation of salivary duct carcinoma, androgen receptor positive.
• Only patients with locally advanced, recurrent or metastatic salivary duct carcinoma can participate.
• Patients must have at least one lesion with a diameter of ≥ 1.5 cm.
• Patients whom intend to start androgen deprivation therapy, after this has been recommended by the treating physician as standard treatment.

Exclusion Criteria:

• Contra-indication for PET imaging (pregnancy, breast feeding severe claustrophobia)
• Impaired renal function: MDRD <30 ml/min/1,73 m2
• Impaired liver function: AST and ALT ALT ≥ 2.5 x ULN (≥5 x ULN for patients with liver metastases)