Advancing Cancer Diagnostics: Evaluating the Potential of Ga-68 FAPi-46 PET Imaging in Solid Tumours

The study “Correlation of 68Ga-FAPi-46 PET Biodistribution with FAP Expression by Immunohistochemistry in Patients with Solid Cancers: Interim Analysis of a Prospective Translational Exploratory Study,” authored by Christine E. Mona et al., is a seminal contribution to the field of nuclear medicine and oncology. Published in the Journal of Nuclear Medicine in July 2022, this research offers an insightful and detailed exploration into the diagnostic potential of 68Ga-FAPi-46 PET imaging in solid cancers.

Background and Objectives

The tumour microenvironment is a critical area of focus in cancer research, given its role in tumour growth, progression, and response to therapy. Within this microenvironment, fibroblast activation protein (FAP) is significantly expressed in cancer-associated fibroblasts (CAFs), which are implicated in various oncogenic processes. Targeting FAP has thus emerged as a promising strategy for both diagnostic and therapeutic applications in oncology.

The primary objective of this study was to evaluate the biodistribution of 68Ga-FAPi-46, a novel PET tracer, and correlate its uptake with FAP expression determined by immunohistochemistry (IHC) in patients with solid cancers. This correlation could validate 68Ga-FAPi-46 PET as a non-invasive imaging technique to assess FAP expression, potentially aiding in patient selection for FAP-targeted therapies and improving personalised treatment strategies.


The study design is a prospective translational exploratory study involving patients with various solid cancers. Participants underwent 68Ga-FAPi-46 PET imaging to map the distribution and intensity of the tracer uptake within their tumours. Following PET imaging, tissue samples were collected for IHC analysis to quantify FAP expression levels. The correlation between PET signal intensity and IHC-determined FAP expression was then analysed.

The methodology’s strength lies in its comprehensive approach, combining advanced imaging techniques with detailed histopathological analysis. By integrating PET imaging with IHC, the researchers aimed to bridge the gap between non-invasive imaging and molecular tumour profiling, providing a holistic view of tumour biology.

Findings and Interpretation

The interim results of the study are promising, demonstrating a robust correlation between 68Ga-FAPi-46 PET biodistribution and FAP expression as determined by IHC. This finding is significant as it supports the hypothesis that 68Ga-FAPi-46 PET can reliably reflect the biological characteristics of the tumour microenvironment. Specifically, higher PET signal intensities corresponded to higher levels of FAP expression, suggesting that 68Ga-FAPi-46 PET could serve as a surrogate marker for FAP expression.

Several key points emerge from these findings:

  • Diagnostic Potential: The ability of 68Ga-FAPi-46 PET to accurately map FAP expression non-invasively underscores its potential as a diagnostic tool. This could lead to earlier and more precise detection of tumours with high FAP expression, guiding treatment decisions and potentially improving patient outcomes.
  • Therapeutic Implications: By identifying patients with high FAP expression, 68Ga-FAPi-46 PET imaging could play a crucial role in stratifying patients for FAP-targeted therapies. This personalised approach could enhance treatment efficacy and reduce unnecessary side effects.
  • Research and Development: The study paves the way for further research into the use of 68Ga-FAPi-46 PET in other cancer types and clinical scenarios. It also opens avenues for the development of new FAP-targeted therapeutics, leveraging the tracer’s ability to pinpoint FAP expression with high accuracy.

Strengths and Contributions

The study’s strengths are manifold, reflecting the authors’ meticulous research design and innovative approach. Some of the most notable strengths include:

  • -Innovative Tracer: The development and utilisation of 68Ga-FAPi-46 as a PET tracer represents a significant advancement in the field of nuclear medicine. Its specificity for FAP provides a novel tool for imaging the tumour microenvironment.
  • Robust Methodology: The combination of PET imaging with IHC analysis ensures that the findings are grounded in non-invasive and molecular biology imaging. This dual approach enhances the validity and reliability of the results.
  • Clinical Relevance: The study addresses a critical need for better diagnostic and therapeutic tools in oncology. By demonstrating the utility of 68Ga-FAPi-46 PET in mapping FAP expression, the research has immediate implications for clinical practice, potentially improving patient care and outcomes.
  • Interdisciplinary Collaboration: The research team comprises experts from various fields, including nuclear medicine, oncology, pathology, and radiology. This interdisciplinary collaboration enriches the study, providing diverse perspectives and expertise.

Limitations and Future Directions

While the interim results are encouraging, the study’s limitations must be acknowledged. The interim nature of the analysis means that the sample size is relatively small, and the findings may not be fully generalisable. Future research should focus on larger, more diverse patient cohorts to validate these initial observations.

Moreover, the long-term outcomes and clinical benefits of 68Ga-FAPi-46 PET imaging need further exploration. Specifically, studies should investigate how this imaging technique influences treatment decisions and patient survival rates over time. Additionally, exploring the potential therapeutic applications of FAP-targeted imaging agents could further enhance their clinical utility.

Future research should also examine the potential of 68Ga-FAPi-46 PET imaging in combination with other diagnostic modalities and therapeutic interventions. For instance, combining PET imaging with other molecular imaging techniques or integrating it into multi-modal treatment regimens could provide a more comprehensive approach to cancer care.


In conclusion, the study by Christine E. Mona and colleagues is a commendable effort that significantly advances the field of nuclear medicine and oncology. The correlation of 68Ga-FAPi-46 PET biodistribution with FAP expression by IHC provides compelling evidence for the utility of this novel imaging technique in solid cancers. The findings suggest that 68Ga-FAPi-46 PET could become a valuable tool for non-invasive tumour profiling, aiding in the early detection and personalised treatment of cancer.

As the study progresses, it is poised to make substantial contributions to cancer diagnostics and treatment. The innovative approach and robust methodology employed by the researchers highlight the importance of integrating advanced imaging techniques into clinical practice. By improving our ability to non-invasively assess tumour biology, this research has the potential to enhance patient outcomes and pave the way for more personalised and effective cancer therapies.

In summary, this study represents a significant step forward in the quest to improve cancer care. It underscores the critical role of innovative imaging techniques in modern oncology and sets the stage for future advancements in the field. The work of Mona et al. is a testament to the power of interdisciplinary collaboration and the ongoing pursuit of excellence in cancer research.


Mona CE, Benz MR, Hikmat F, Grogan TR, Lueckerath K, Razmaria A, Riahi R, Slavik R, Girgis MD, Carlucci G, Kelly KA, French SW, Czernin J, Dawson DW, Calais J. Correlation of 68Ga-FAPi-46 PET Biodistribution with FAP Expression by Immunohistochemistry in Patients with Solid Cancers: Interim Analysis of a Prospective Translational Exploratory Study. J Nucl Med. 2022 Jul;63(7):1021-1026.

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