Interlesional Heterogeneity Between [⁶⁸Ga]Ga-DOTATATE and [⁶⁸Ga]Ga-FAPI-04 PET/CT After [¹⁷⁷Lu]Lu-DOTATATE PRRT in...

Area of Science:

• Nuclear Medicine
• Oncology
• Radiopharmaceutical Therapy

Background:

• Theranostics, utilizing somatostatin receptor (SSTR)-based PET/CT and radiopharmaceutical therapy, is standard for well-differentiated neuroendocrine tumors (NETs).
• SSTR-based PET/CT can fail to detect disease progression post-therapy due to SSTR downregulation or tumor grade changes.
• Fibroblast activation protein inhibitor (FAPI) PET/CT is emerging as a potential imaging modality for highly proliferative NETs.

Purpose of the Study:

• To illustrate a unique case of pancreatic neuroendocrine tumor (NET) with progressive metastatic disease after peptide receptor radionuclide therapy.
• To evaluate the utility of [68Ga]Ga-FAPI-04 PET/CT in a case of advanced NET with variable tracer avidity.
• To explore FAPI PET/CT as a complementary diagnostic tool in NET theranostics.

Main Methods:

• Case report of a patient with grade II pancreatic NET and metastatic disease.
• Utilized [68Ga]Ga-DOTATATE PET/CT to assess somatostatin receptor expression.
• Employed [68Ga]Ga-FAPI-04 PET/CT to evaluate fibroblast activation protein expression in tumor lesions.

Main Results:

• The patient presented with progressive liver and skeletal metastases after peptide receptor radionuclide therapy, with increased tumor grade (Ki-67 40%-50%).
• [68Ga]Ga-DOTATATE PET/CT showed no SSTR uptake in liver lesions, indicating SSTR downregulation.
• [68Ga]Ga-FAPI-04 PET/CT revealed intense tracer avidity in liver lesions and non-avid skeletal lesions, highlighting heterogeneity.

Conclusions:

• [68Ga]Ga-FAPI-04 PET/CT can detect FAPI-avid lesions, offering complementary information to SSTR-based imaging in NETs.
• FAPI PET/CT may serve as a valuable imaging modality for high-proliferative NETs.
• FAPI PET/CT could be considered as part of a new theranostic approach alongside SSTR-based therapies for NET patients.