Detecting Fibroblast Activation Proteins in Lymphoma Using 68Ga-FAPI PET/CT.

Cancer-associated fibroblasts that overexpress fibroblast activation protein (FAP) are enriched in many epithelial carcinomas and in hematologic neoplasms. PET/CT with radiolabeled FAP inhibitor (FAPI) is a new diagnostic tool for visualizing the tumor stroma. This prospective study aimed to profile FAPs in different subtypes of lymphomas and explore the potential utility of 68Ga-FAPI PET/CT in lymphomas.

Methods

In this prospective study, we recruited 73 lymphoma patients who underwent 68Ga-FAPI PET/CT and recorded and measured semiquantitative parameters and ratios of their scan results. FAPI expression was assessed by immunochemistry in samples obtained from 22 of the lymphoma patients.

Results

We evaluated 11 patients with Hodgkin lymphoma and 62 with non-Hodgkin lymphoma (NHL). Significantly elevated FAP uptake was observed in Hodgkin lymphoma lesions, correlating with the intensity of FAP immunostaining (score, 3+). A positive association was found between the corresponding clinical classification of NHL and the 68Ga-FAPI uptake activity of the lesion. Aggressive NHL lesions, with moderate to strong FAP immunostaining (score, 2+ to 3+), exhibited intense to moderate 68Ga-FAPI uptake. Indolent NHL lesions showed weak FAP staining and mild to moderate 68Ga-FAPI uptake. No statistically significant correlation emerged between the sum of the product of the diameters and the corresponding SUVmax (P = 0.424). The tumor-to-liver ratios were 6.26 ± 4.17 in indolent NHL and more than 9 in other subtypes.

Conclusion

68Ga-FAPI imaging can be used to detect FAP expression in lymphoma lesions and may be an alternate method for characterizing lymphoma profiles.