FAP and lupus nephritis: 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.