Purpose:
F18-Fluciclovine is a synthetic amino acid tracer currently FDA approved for prostate cancer imaging. Case reports have documented its ability to detect oropharyngeal squamous cell carcinoma (SCC). This study prospectively evaluates the ability of Fluciclovine to detect the site of primary in patients presenting with biopsy proven neck nodal metastatic SCC but with no primary site detected on contrast enhanced (CE) CT of the neck.

Materials and Methods:
Nine patients with metastatic SCC cervical lymphadenopathy and no known primary were studied. All patients underwent CE-CT, standard of care (SOC) FDG PET/CT and Fluciclovine PET/CT. The imaging studies were reviewed by neuroradiology and nuclear medicine board-certified radiologists. A region of interested was drawn surrounding the site of suspected primary and contralateral background mucosa, recording the maximum standard uptake value (SUVmax). A lesion to background (L/B) was calculated. Each suspected primary site was then classified according to subjective 5-point Likert score: Not confident of primary location (Likert 1) through very confident (Likert 5). The patients then underwent examination under anesthesia with biopsies taken of suspected primary sites identified on FDG and Fluciclovine PET as well as any clinically suspicious sites.

Results:
Fluciclovine identified a suspected primary site in 7/9 patients. FDG identified a primary site in 8/9 patients. In 8/9 patients the FDG PET and Fluciclovine PET _ndings were concordant and in 1 a suspected primary was seen on FDG but not on Fluciclovine. Pathology was positive and concordant with suspected primary site identi_ed on PET in 5 patients. In 1 patient, pathology was positive despite negative PET scans. 1 patient had Fluciclovine and FDG scans which revealed a possible primary with negative pathology. A higher Likert score correlated well with identifying site of primary. 5/5 patients with Likert score of 3 or greater on Fluciclovine PET had positive pathology, while both patients with Likert score of 1 or 2 and both patients with no primary identified had negative pathology.

Conclusions:
Fluciclovine PET demonstrated a nearly-equivalent ability to SOC FDG PET in identifying the site of primary tumor in patients with metastatic SCC of the head and neck but no apparent primary seen on CE-CT. Additional data is needed to confirm these initial observations.

Identification of Primary Site of Malignancy in Squamous Cell Carcinoma of the Head and Neck with Unknown Primary using F-18 Fluciclovine PET/CT: Preliminary Results of a Pilot Study

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