FAP is considered a relatively clean target, as its expression is restricted to the tumor microenvironment and tumor draining lymph nodes (Juillerat-Jeanneret et al., 2017; Denton et al., 2014), with little to no on-target-off-tumor toxicity expected as demonstrated in clinical trials with FAP-4-1BBL (Melero et al., 2023). This evidence concerns the gene FAP and neoplasm.