CXCR4 and neuroendocrine carcinoma: We aimed to elucidate the diagnostic potential of the C-X-C motif chemokine receptor 4 (CXCR4)-directed positron emission tomography (PET) tracer <sup>68</sup>Ga-Pentixafor in patients with poorly differentiated neuroendocrine carcinomas (NEC), relative to the established reference standard <sup>18</sup>F-FDG PET/computed tomography (CT).