New radiotracers may gain ground in FDG territory

PET/CT with the radiotracer 18F-FDG may have met its match at cancer detection in two new “FAPI” tracers based on gallium-68. The acronym stands for fibroblast activation protein inhibitor, and in a recent trial the new tracers equaled or bettered FDG PET/CT on image quality, required no fasting and yielded images in less time than FDG PET/CT.

The proof-of-concept study is running in the March edition of the Journal of Nuclear Medicine.

Frederik Giesel, MD, MBA, of the University of Heidelberg in Germany and colleagues based their FAPI hypothesis on the abnormally large amounts of the fibroblast activation protein (FAP) in cancer-associated fibroblasts (CAFs). The presence of elevated FAP is associated with fast tumor growth, migration and progression.  

CAFs turn up in more than 90 percent of epithelial carcinomas—including breast, lung, colon, pancreatic, and head and neck cancers. This near ubiquity makes them “an attractive target for both diagnostic imaging and therapy,” according to a news item published by the Society of Nuclear Medicine & Molecular Imaging.

CAFs also are more stable than cancer cells, making them less likely to develop resistance to therapy, according to SNMMI.

For the study, Giesel and colleagues scanned 50 patients who were referred by oncologists after standard diagnostic testing proved inconclusive.

All 50 patients tolerated the new agents—68Ga-FAPI-2 and 68Ga-FAPI-4—and the substances’ fast action enabled the researchers to obtain images with quicker than normal scans and short wait times after tracer injection.  

“For those who are facing unmet diagnostic challenges—unclear tumor segmentation for radiation therapy, suspicion of false-negative findings, or selection of last-line experimental treatment—68Ga-FAPI may help to provide answers,” said senior author Uwe Haberkorn, MD.

Haberkorn added that the FAPI tracers may find uses beyond cancer care, as they show potential to aid in the assessment and management of cardiac diseases or fibrotic diseases of the lung, liver and kidneys.