Non-oncologic incidental uptake on FAPI PET/CT imaging

Area of Science:

• Nuclear Medicine
• Oncology
• Radiochemistry

Background:

• Fibroblast activation protein (FAP) is a key marker in cancer-associated fibroblasts (CAFs), linked to tumor progression.
• Radiolabeled FAP inhibitors (FAPI) enable PET/CT imaging, offering high tumor-to-background ratios.
• Increasing FAPI PET/CT studies reveal incidental findings in non-oncologic conditions.

Purpose of the Study:

• To review physiological and non-oncologic FAPI uptake patterns across organ systems.
• To aid accurate interpretation of FAPI PET/CT scans.
• To guide management of incidental FAPI uptake findings.

Main Methods:

• Systematic literature review of FAPI PET/CT studies (FAPI-02, FAPI-04, FAPI-46).
• Analysis of FAPI uptake patterns in various organ systems.
• Inclusion of institutional case examples from UCLA.

Main Results:

• FAPI uptake is observed in diverse non-oncologic conditions, including benign tumors, fibrosis, inflammation, and degenerative diseases.
• Specific uptake patterns are detailed for multiple organ systems.
• Knowledge of these patterns is essential for differentiating from malignant disease.

Conclusions:

• Accurate interpretation of FAPI PET/CT requires understanding physiological and non-oncologic uptake.
• This knowledge is vital for appropriate patient management, especially in cancer staging.
• FAPI PET/CT has potential beyond oncology, highlighting the need for comprehensive interpretation guidelines.