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Novel Diagnostics and Bioinfomatics

(P 220) [68GA]GA-FAPI PET/CT AS NOVEL DIAGNOSTIC TOOL IN SARCOMA

Location: The Liffey, Level 1

    Author(s)

  • Rainer Hamacher, MD

    Medical Oncology
    Department of Medical Oncology, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

    • Co-Author(s)

  • Helena Lanzafame, MD (she/her/hers)

    Researcher
    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • IM

    Ilektra A. Mavroeidi, MD

    Resident doctor
    Department of Medical Oncology, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • Kim M. Pabst, MD (she/her/hers)

    Physician in training
    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • NH

    Nader Hirmas, MD

    PhD Candidate
    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • LK

    Lukas Kessler, MD

    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • Sebastian Bauer, MD (he/him/his)

    Attending, Director Sarcoma Center
    Department of Medical Oncology, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • LP

    Lars-Erik Podleska, MD

    Department of Musculoskeletal Oncology, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • KH

    Ken Herrmann, MD

    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • JS

    Jens T. Siveke, MD

    Bridge Institute of Experimental Tumor Therapy, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

  • WF

    Wolfgang P. Fendler, MD

    Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen
    Essen, Nordrhein-Westfalen, Germany

Objective: Radiolabeled fibroblast activation protein (FAP) inhibitors (68Ga-FAPI-46) show high tumor uptake on PET in several tumor entities and therefore represent a promising novel molecular imaging method in oncology besides 18F-FDG PET. This is particularly interesting for bone sarcomas (BS) and soft-tissue sarcomas (STS) that demonstrate high expression of FAP on tumor cells and associated fibroblasts. Here we aimed to investigate the diagnostic performance of FAP-directed 68Ga-FAPI PET/CT in BS and STS and compared it to 18FDG PET/CT.

Methods: Patients with BS or STS undergoing clinical 68Ga-FAPI PET for staging/restaging were eligible for enrollment into the 68Ga-FAPI PET prospective observational trial. A group of patients also underwent 18F-FDG PET. Number of detected lesions and tracer uptake (SUVmax) for T, N and M were analyzed. Non-parametrical t-test was employed for semiquantitative analysis. Association between 68Ga-FAPI PET uptake and histopathologic FAP expression was analyzed with Spearman r correlation.

Results: We included 200 sarcoma patients (65 BS, 135 STS), of which 32 (16%) were low, 141 (71%) were high-grade sarcomas and 27 (14%) sarcoma entities for which grading doesn’t apply (N/A). 68Ga-FAPI vs. 18F-FDG PET detected a total of 1174 (81%) vs. 1023 (71.5%) lesions. On a per-region basis, 68Ga-FAPI vs. 18F-FDG PET demonstrated higher detection efficacy for T (144 (100%) vs. 124 (86%) lesions) and M (1167 (97%) vs. 1026 (86%) lesions). Moreover, we observed as well a higher sensitivity (96% vs. 88%), specificity (88% vs. 60%), PPV (99% vs. 95%), NPV (68% vs. 38%) and overall accuracy (95% vs. 88%) for 68Ga-FAPI when compared to 18F-FDG. Radiotracer uptake (SUVmax) was significantly higher for 68Ga-FAPI vs. 18F-FDG in low grade (10.4±8.5 vs. 7.1±4.5, p=0.01) and N/A (22.3±12.2 vs. 8.6±10.8, p=0.004) tumors as well as in patients with SFT (T: SUVmax 23.5±11.9 vs. 4.5±8.7, p=0.0005; M: SUVmax 17.±28.7 vs. 3.8±2.0, p=0.0001) and myxoid liposarcoma(T: SUVmax 5.6±12.2 vs. 3.5±2.1, p=0.04). The association of 68Ga-FAPI uptake and histopathologic FAP expression (n = 89) showed a moderate positive correlation (Spearman r = 0.43; p < 0.0002).

Conclusion: 68Ga-FAPI PET/CT is as novel imaging tool for sarcoma and shows superiority over 18F-FDG PET/CT particularly in low grade sarcoma.