# Expanding horizons: radiolabeled FAPI in imaging of autoimmune diseases

## TL;DR

This paper reviews how radiolabeled FAPI PET can be used to image fibroblast activation in autoimmune diseases, expanding its potential beyond cancer.

## Contribution

The paper systematically evaluates FAPI PET's diagnostic potential in autoimmune diseases, highlighting its broader applicability.

## Key findings

- FAPI PET can image fibroblast activation in autoimmune diseases with chronic inflammation.
- FAPI's use in oncology suggests potential for similar applications in autoimmune conditions.
- Technical advantages of FAPI PET include its ability to provide in vivo assessments of fibroblast activity.

## Abstract

Fibroblast activation protein alpha (FAP) is a type II transmembrane protease that exhibits both dipeptidyl peptidase and endopeptidase activities. It is upregulated in activated fibroblasts, particularly in tumor stroma and in fibrotic processes associated with various benign conditions. Recent studies have revealed that FAP is also highly expressed in certain Autoimmune Diseases (AIDs) characterized by chronic inflammation and tissue remodeling. Small-molecule inhibitors targeting FAP (FAPI) positron emission tomography (PET) provides a direct imaging modality for assessing fibroblast activation in vivo. FAPI’s application in oncology has attracted considerable attention in nuclear medicine. However, evidence supporting its efficacy in AIDs remains limited. This review systematically evaluates the diagnostic and phenotyping potential of FAPI PET in AIDs, expands its applications across a broader disease spectrum, highlights technical advantages, and delineates future research directions.