FAPI PET uptake patterns after invasive medical interventions: a single center retrospective analysis

Peter George Maliha; Masatoshi Hotta; Andrea Farolfi; Tristan Grogan; Rejah Alano; Andrea Limon; Ethan Lam; Giuseppe Carlucci; Shadfar Bahri; Ali Salavati; Matthias Benz; Daniel Silverman; Pawan Gupta; Andrew Quon; Martin Allen-Auerbach; Johannes Czernin; Jeremie Calais

doi:10.1007/s00259-024-06733-7

FAPI PET uptake patterns after invasive medical interventions: a single center retrospective analysis

Eur J Nucl Med Mol Imaging. 2024 May 16. doi: 10.1007/s00259-024-06733-7. Online ahead of print.

Authors

Peter George Maliha^{1

2

3}, Masatoshi Hotta^{4

5}, Andrea Farolfi^{4

6}, Tristan Grogan⁷, Rejah Alano⁴, Andrea Limon⁴, Ethan Lam⁴, Giuseppe Carlucci⁴, Shadfar Bahri⁴, Ali Salavati⁴, Matthias Benz⁴, Daniel Silverman⁴, Pawan Gupta⁴, Andrew Quon⁴, Martin Allen-Auerbach⁴, Johannes Czernin⁴, Jeremie Calais⁴

Affiliations

¹ Ahmanson Translational Theranostics Division, Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA, USA. peter.maliha@mail.mcgill.ca.
² Nuclear Medicine, Centre de recherche du Centre Hospitalier de l'Université de Montréal, Université de Montréal, Montréal, Québec, Canada. peter.maliha@mail.mcgill.ca.
³ Nuclear Medicine Department, Centre Hospitalier de l'Université de Montréal, Montréal, Québec, Canada. peter.maliha@mail.mcgill.ca.
⁴ Ahmanson Translational Theranostics Division, Department of Molecular & Medical Pharmacology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA, USA.
⁵ Department of Nuclear Medicine, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-Ku, Tokyo, 162-8655, Japan.
⁶ Nuclear Medicine, IRCCS Azienda Ospedaliero-Universitaria Di Bologna, Bologna, Italy.
⁷ Department of Medicine Statistics Core, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA, USA.

PMID: 38750372
DOI: 10.1007/s00259-024-06733-7

Abstract

Purpose: Fibroblast activation protein (FAP)-inhibitor (FAPI)-PET tracers allow imaging of the FAP-expressing cancer associated fibroblasts (CAF) and also the normal activated fibroblasts (NAF) involved in inflammation/fibrosis that may be present after invasive medical interventions. We evaluated [68Ga]Ga-FAPI-46 uptake patterns post-medical/invasive non-systemic interventions.

Methods: This single-center retrospective analysis was conducted in 79 consecutive patients who underwent [⁶⁸Ga]Ga-FAPI-46 PET/CT. Investigators reviewed prior patient medical/invasive interventions (surgery, endoscopy, biopsy, radiotherapy, foreign body placement (FBP) defined as implanted medical/surgical material present at time of scan) and characterized the anatomically corresponding FAPI uptake intensity both visually (positive if above surrounding background) and quantitatively (SUVmax). Interventions with missing data/images or confounders of [⁶⁸Ga]Ga-FAPI-46 uptake (partial volume effect, other cause of increased uptake) were excluded. Available correlative FDG, DOTATATE and PSMA PET/CTs were analyzed when available.

Results: 163 medical/invasive interventions (mostly surgeries (49%), endoscopies (18%) and non-surgical biopsies (10%)) in 60 subjects were included for analysis. 43/163 (26%) involved FBP. FAPI uptake occurred in 24/163 (15%) of interventions (average SUVmax 3.2 (mild), range 1.5-5.1). The median time-interval post-intervention to FAPI-PET was 47.5 months and was shorter when FAPI uptake was present (median 9.5 months) than when absent (median 60.1 months; p = 0.001). Cut-off time beyond which no FAPI uptake would be present post-intervention without FBP was 8.2 months, with a sensitivity, specificity, positive predictive value and negative predictive value of 82, 90, 99 and 31% respectively. No optimal cutoff point could be determined when considering interventions with FBP. No significant difference was detected between frequency of [⁶⁸Ga]Ga-FAPI-46 and [¹⁸F]FDG uptake in intervention sites. Compared to [⁶⁸Ga]Ga-PSMA-11, [⁶⁸Ga]Ga-FAPI-46 revealed more frequent and intense post-interventional tracer uptake.

Conclusion: [⁶⁸Ga]Ga-FAPI-46 uptake from medical/invasive interventions without FBP appears to be time dependent, nearly always absent beyond 8 months post-intervention, but frequently present for years with FBP.

Keywords: FAPI; Fibroblast; Intervention; PET/CT; Pitfall.