[68Ga]Ga‑FAPI PET/CT in the evaluation of Langerhans cell histiocytosis: comparison with [18F]FDG PET/CT

Abstract

Purpose

We aimed to explore the value of [⁶⁸Ga]Ga‑FAPI PET/CT for the evaluation of Langerhans cell histiocytosis (LCH) in comparison with [¹⁸F]FDG PET/CT.

Methods

Thirty-two patients pathologically diagnosed with LCH were enrolled in this study. [⁶⁸Ga]Ga‑FAPI and [¹⁸F]FDG PET/CT were performed within 1 week to identify disease extent and status. The detectability and intensity of the involved organs were compared between these two tracers.

Results

Thirty patients had active disease while two had non-active disease. In patients with active disease, the most commonly involved organ was bone (27/30), and [⁶⁸Ga]Ga-FAPI PET/CT detected more osseous lesions (106/106) than [¹⁸F]FDG PET/CT (52/106). [⁶⁸Ga]Ga-FAPI also identified liver, skin, and salivary gland involvement, which were often missed by [¹⁸F]FDG. Although both tracers detected thymus and pituitary gland involvement, [⁶⁸Ga]Ga-FAPI demonstrated higher image contrast and more diagnostic confidence. Lymph node involvement, however, was not visualized by [⁶⁸Ga]Ga-FAPI. Due to the superior sensitivity of [⁶⁸Ga]Ga-FAPI, approximately 30% (10/30) of patients experienced reclassification in disease status or subtype. Furthermore, [⁶⁸Ga]Ga‑FAPI appeared to be advantageous in response assessment.

Conclusion

[⁶⁸Ga]Ga-FAPI PET/CT outperforms [¹⁸F]FDG PET/CT in detecting osseous and extra-nodal lesions in LCH, providing a valuable tool for precise disease evaluation and treatment planning.