CGA and neuroendocrine carcinoma: Within the subgroups NET and NEC, statistically significant differences could be observed between the determination of serum levels of CgA (p = 0.013), the immunohistochemical assessment of ISLET-1 (p = 0.043), CD56 (p = 0.005) and serotonin (p = 0.015) and FDG- (p = 0.001) or SSTR-PET-based imaging (p < 0.0001).