*3.1. Somatostatin Receptor (SSTR)-Targeting Probes*

Somatostatin receptors have become typical therapeutic targets in neuroendocrine tumors (NETs) because they are often overexpressed on the surface of tumor cells. This

has led to the development of several 68Ga-labelled somatostatin analogs as PET imaging probes [81], which could be used for the diagnosis of MTC [80]. 68Ga-labeled somatostatin analogs, including [68Ga]Ga-DOTA-(1-Nal3)-octreotide ([68Ga]Ga-DOTANOC), [ 68Ga]Ga-DOTA(0)-Phe(1)-Tyr(3)-octreotide ([68Ga]Ga-DOTATOC), and [68Ga]Ga-DOTA- (Tyr3)-octreotate ([68Ga]Ga-DOTATATE), are valuable diagnostic tools showing excellent performance in the majority of patients with NETs [82]. Nevertheless, studies reporting the diagnostic value of SSTR-targeted PET in recurrent MTC are limited. A meta-analysis involving nine studies reported that the tumor detection rate on SSTR-based PET or PET/CT is only 63.5% in recurrent MTC, which is lower than that in other NETs [83].
