Cholecystokinin-2 (CCK2) receptor is overexpressed in more than 90% of MTC cases, and preclinical studies have shown that 68Ga-MGS5 (targeting CCK2) has good stability in vivo and is promising for diagnosis and staging of MTC. This prospective study will compare the diagnostic effects of 68Ga-MGS5 and 68Ga-DOTATATE on MTC primary foci, lymph node metastasis, and distant metastasis, and explore the effect of 68Ga-MGS5 PET/CT on the clinical staging (TNM staging) of MTC.

This study was planned to enroll 20 patients with suspected MTC and MTC recurrence who attended the First Hospital of Fujian Medical University from June 2023 onwards. Each patient completed PET/CT examination within 1 week, one 68Ga-DOTATATE PET/CT whole-body examination and two 68Ga-MGS5 PET/CT whole-body examinations (1 hour and 2 hours after injection, respectively). CCK2 immunohistochemical staining and expression scoring of primary foci and lymph node metastases were also performed.

Inclusion Criteria:

• Patients of either gender, aged ≥ 18 years and ≤80 years.
• Patients with pathologic findings confirming the diagnosis of MTC
• Patients with MTC recurrence
• Signed written consent

Exclusion Criteria:

• Pregnant or breastfeeding female patients
• Patients with claustrophobic behavior
• The inability or unwillingness of the research participant, parent or legal representative to provide written informed consent