FAP-expression of SF from OA and rheumatoid arthritis (RA) (15 OA- and 26 RA-patients) were analyzed by single-cell cytometry by time of flight (cyTOF).<h4>Results</h4>148 of 268 patients (55.2%) showed increased joint-associated FAPI-uptake (average SUVmax/mean of 3.25 ± 1.28/ 1.94 ± 0.70). This evidence concerns the gene FAP and rheumatoid arthritis.