A retrospective evaluation published in EJNMMI Research demonstrates that fibroblast activation protein inhibitor imaging using single-photon emission computed tomography combined with computed tomography achieved higher sensitivity and diagnostic accuracy for detecting bone metastases than conventional computed tomography. In an analysis comparing imaging modalities across patients with advanced malignancies, the targeted tracer approach demonstrated a sensitivity of 96.5 percent and an overall accuracy of 95.9 percent, significantly exceeding the 59.7 percent sensitivity and 67.1 percent accuracy observed with conventional computed tomography.
The investigation utilized data from an established clinical registry registered under ChiCTR2100048093 in June 2021 to examine the clinical performance of the radiotracer designated as technetium-99m labeled H7ND. Between June 2021 and September 2023, investigators screened 564 patients presenting with malignancies who had undergone fibroblast activation protein inhibitor imaging. From this broader screening group, the researchers enrolled a cohort of 80 individuals presenting with either confirmed or suspected skeletal metastases, of whom 64 were subsequently confirmed to have bone metastases. The patient group included 48 men, with a median age of 60 years and an age distribution ranging from 23 to 79 years.
Direct comparisons between diagnostic modalities revealed that the fibroblast activation protein inhibitor scan detected significantly more metastatic skeletal lesions than both conventional computed tomography and magnetic resonance imaging. Alongside the statistically significant improvement over computed tomography, lesion identification surpassed magnetic resonance imaging with a confirmed significance level of p equals 0.041. Furthermore, when evaluated against standard planar bone scintigraphy, the molecular imaging technique identified additional metastatic lesions in skeletal regions characterized by osteolytic and mixed structural features, uncovering 12 additional osteolytic lesions and 9 additional mixed lesions that had escaped detection on standard bone scans.
Tracer uptake within metastatic sites varied markedly depending on the biological and structural subtype of the skeletal lesion, exhibiting a statistically significant difference across categories with a p-value below 0.001. Quantitative assessments of tracer concentration revealed that osteolytic metastases displayed the highest uptake, recording a median maximum standardized uptake value of 13.41. Mixed metastases exhibited an intermediate uptake level with a median maximum standardized uptake value of 10.78, whereas osteoblastic metastases demonstrated substantially lower radiotracer concentration, registering a median maximum standardized uptake value of 2.70.
Beyond anatomical detection, the integration of fibroblast activation protein inhibitor imaging altered clinical assessment relative to conventional multi-modality combinations, revealing previously undetected lesions in 46.3 percent of the evaluated patients. These newly identified metastatic foci prompted documented treatment modifications in 86.5 percent of the affected cases. For individuals within the cohort who underwent longitudinal follow-up scanning, serial changes in the maximum standardized uptake values of skeletal metastases correlated with therapeutic response evaluations determined by standard RECIST 1.1 criteria.
The authors emphasized that while these findings indicate enhanced diagnostic capability across cancer types, particularly for osteolytic and mixed skeletal metastases, the conclusions remain tempered by inherent methodological constraints. Because the investigation was designed as a single-center retrospective study drawn from registry records, the authors highlighted that preliminary observations regarding treatment monitoring represent exploratory findings that require further validation.
The clinical rationale for investigating fibroblast activation protein inhibitor imaging centers on the substantial burden imposed by secondary skeletal disease. Bone metastases frequently occur in advanced-stage malignancies, contributing directly to diminished quality of life and unfavorable prognoses for affected patients. Furthermore, conventional imaging modalities currently relied upon for diagnosing bone metastases exhibit inherent limitations in clinical practice. To address these diagnostic challenges across various cancer types, the research cohort was established to evaluate the diagnostic utility of fibroblast activation protein inhibitor imaging utilizing [99mTc]Tc-H7ND.
Alongside comparisons with CT, MRI, and bone scintigraphy, the diagnostic evaluation incorporated comparative assessments against [18F]FDG PET/CT. In addition to measuring general detection rates across malignancies, the study protocol specifically assessed radiotracer uptake values across different components of bone metastases to clarify how the tracer behaves across structural subtypes.
Beyond initial detection, the researchers incorporated discussions on the potential of FAPI imaging in evaluating treatment response. The investigation relied on a single-center real-world cohort with registry data formally recorded on the registration date of June 30, 2021. While the reported findings may enhance diagnostic performance in detecting bone metastases across malignancies, particularly for osteolytic and mixed metastases, preliminary observations also suggest possible applications in monitoring therapeutic response. However, the authors concluded that further validation is required to confirm these exploratory findings.
Subject of Research: Diagnostic utility of FAPI SPECT/CT imaging for detecting bone metastases in cancer patients
Article Title: Retrospective study of FAPI imaging in bone metastases: diagnostic utility and therapeutic relevance across cancer types in a single-center real-world cohort
Article References: Li, X., Jia, X., Li, C., Deng, H., Tian, T., Zhao, W., Fu, X., Wang, Y., Liu, Y., Yang, A., Jia, B., & Gao, R. (2026). Retrospective study of FAPI imaging in bone metastases: diagnostic utility and therapeutic relevance across cancer types in a single-center real-world cohort. EJNMMI Research, 16(1), Article 156. https://doi.org/10.1186/s13550-026-01502-z
Image Credits: AI Generated
DOI: 10.1186/s13550-026-01502-z
Keywords: FAPI imaging, bone metastases, SPECT/CT, [99mTc]Tc-H7ND, computed tomography, magnetic resonance imaging, bone scintigraphy, [18F]FDG PET/CT, osteolytic metastases, osteoblastic metastases, mixed metastases, SUVmax, RECIST 1.1, cancer staging, treatment modification, fibroblast activation protein inhibitor, retrospective cohort study
News Source: Nathaniel Bowman. (November 11, 2026). FAPI SPECT Scans Improve Bone Metastasis Detection Across Malignancies in Retrospective Study. Scienmag.
