Researchers in China say a new radiotracer may be more effective than the most commonly used radiopharmaceutical for detecting multiple cancers.

While the workhorse radiotracer 18F-FDG identified 80% of primary tumors across multiple cancer types, 68Ga-FAP-2286 identified 100% and was more effective in detecting lymph node metastases and distant metastases, the scientists said in their study. They attribute the variation to the radiotracer's different targets, with 18F-FDG measuring glucose metabolism and 68Ga-FAP-2286 targeting fibroblast activation protein (FAP). Because it’s over-expressed in cancer cells, recent innovations have shown that FAP may be better when imaging solid tumors.

The researchers assessed 64 patients with 14 cancer types. Sixty-three were paired with 68Ga-FAP-2286 and 18F-FDG PET/CT, and 19 with 68Ga-FAP-2286 and 68Ga-FAP-46 (another 68Ga-radiolabeled variant).
In addition to detecting more tumors, 68Ga-FAP-2286 PET had a higher radiotracer uptake and tumor-to-background ratio than 18F-FDG. Similar clinical results were found in the group with 68Ga-FAP-2286 and 68Ga-FAPI-46.

"In the next step, we are going to evaluate the diagnostic accuracy of 68Ga-FAPI-RGD PET/CT in a larger number of patients. Additionally, it is important to note that this study primarily focused on tumor lesion detection rates; we will also evaluate the specificity of 68Ga-FAPI-RGD PET/CT with histopathological confirmation (via surgery or biopsy) in a larger patient cohort," Dr. Haojun Chen, nuclear medicine physician at the First Affiliated Hospital of Xiamen University in Xiamen, China, told HCB News.

68Ga-FAP-2286 showed promise for safely diagnosing, staging and restaging cancer, according to Chen, who says it may be a better alternative for diagnosing cancers that show low-to-moderate uptake of 18F-FDG, such as head and neck, gastric, pancreatic and liver tumors.

Additionally, he says it could be paired with 177Lu as a targeted radionuclide therapy, in which a radioactive chemical is paired to a cell-targeting molecule and injected into the body.

But he warns that compared to 18F-FDG, 68Ga-FAP-2286 exhibited some limitations. "There is high uptake and similar retention of FAPI in inflammatory and malignant processes, leading to potential false positive interpretations without careful attention to the clinical context. In some situations, FAPI revealed more false positive findings than FDG, particularly in the diagnosis of bone lesions, including osteofibrous dysplasia, degenerative bone disease, periodontitis, arthritis."

Additionally, differentiation of viable tumors from inflammatory or fibrotic processes could be challenging when undertaking FAPI post-therapy assessments, and for hematological neoplasm, FAPI PET/CT demonstrated a lower activity and detection rate for multiple myeloma and lymphoma than did 18F-FDG PET/CT.

The study, PET imaging of fibroblast activation protein in various types of cancers by using 68Ga-FAP-2286: Comparison with 18F-FDG and 68Ga-FAPI-46 in a single-center, prospective study was published in the March issue of The Journal of Nuclear Medicine.

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