Although previous studies have reported higher FAP expression on FAP PET in diseases associated with renal fibrosis—such as [68Ga]Ga-FAPI-04 in lupus nephritis (SUVmean of 2.8 vs. 1.5 in healthy controls (15)) and [18F]AlF-NOTA-FAPI-04 in IgA nephropathy (SUVmean of 3.6 vs. 1.5 in controls (16))—this was not reflected in the immunohistochemistry results of our patient with rapidly progressive glomerulonephritis type 3. This evidence concerns the gene FAP and renal fibrosis.