CXCR4-Directed PET/CT in Patients with Newly Diagnosed Neuroendocrine Carcinomas.

We aimed to elucidate the diagnostic potential of the C-X-C motif chemokine receptor 4 (CXCR4)-directed positron emission tomography (PET) tracer Ga-Pentixafor in patients with poorly differentiated neuroendocrine carcinomas (NEC), relative to the established reference standard F-FDG PET/computed tomography (CT). In our database, we retrospectively identified 11 treatment-naïve patients with histologically proven NEC, who underwent F-FDG and CXCR4-directed PET/CT for staging and therapy planning. The images were analyzed on a per-patient and per-lesion basis and compared to immunohistochemical staining (IHC) of CXCR4 from PET-guided biopsies. Ga-Pentixafor visualized tumor lesions in 10/11 subjects, whileF-FDG revealed sites of disease in all 11 patients. Although weak to moderate CXCR4 expression could be corroborated by IHC in 10/11 cases, F-FDG PET/CT detected significantly more tumor lesions (102 vs. 42; total lesions, = 107; < 0.001). Semi-quantitative analysis revealed markedly higher F-FDG uptake as compared to Ga-Pentixafor (maximum and mean standardized uptake values (SUV) and tumor-to-background ratios (TBR) of cancerous lesions, SUV: 12.8 ± 9.8 vs. 5.2 ± 3.7; SUV: 7.4 ± 5.4 vs. 3.1 ± 3.2, < 0.001; and, TBR 7.2 ± 7.9 vs. 3.4 ± 3.0, < 0.001). Non-invasive imaging of CXCR4 expression in NEC is inferior to the reference standard F-FDG PET/CT.