A pilot study of PSMA-targeted F-18-DCFPyL PET imaging of patients with adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a rare malignancy of the salivary glands with poor long-term outcomes and with a need for improved imaging and therapeutic options. Prostate-specific membrane antigen (PSMA) expression has been observed in ACC and preliminary studies have demonstrated PET imaging using 68Ga-functionalized PSMA agents for positron emission tomography (PET). We aimed to assess the extent of PSMA expression in a collection of archival ACC samples and demonstrate the feasibility of using 18F-DCFPyL for PSMA PET imaging of ACC. PSMA expression levels were assessed in 77 ACC and 11 unaffected parotid gland control samples by immunohistochemistry and quantified by mean H-score. Three patients with metastatic ACC, who had previously undergone local resection, were imaged with18F-DCFPyL PSMA PET in a prospective, pilot trial setting. Demographic, oncologic, and treatment history from the PET patient cohort were acquired at the time of imaging. Maximum standardized uptake values (SUVmax) were obtained from representative presumptive metastatic lesions on the 18F-DCFPyL scans by manual placement of regions-of-interest. PSMA expression was detected in 52% of archival ACC samples, compared to 18% in the unaffected salivary glands. Moderate or high levels of PSMA expression (H-score > 5) were seen in 37% of samples. Radiotracer avid disease was identified on PET imaging of all three patients with tumor SUVmax values of 4.1, 4.0, and 2.0, corresponding to tumor-to-liver ratios of 0.7, 1.0, and 0.4 respectively. We find that PSMA is expressed in a majority of histologic samples from patients with ACC. We also demonstrated the feasibility of 18F-DCFPyL PSMA-targeted PET imaging in the assessment of ACC. Overall, the tumor uptake on 18F-DCFPyL PET was modest compared to lesional uptake seen in prostate cancer. Given the potential role of PSMA-targeted agents in the management of ACC, broadening access to PSMA PET through F-18-labeled PSMA PET agents is important. Clinical trials investigating the use of PSMA-targeted radioligand therapies for ACC are underway.