FAP and neoplasm: First, as a scenario that may offer part of the explanation for the differing efficacies or the lack of effect of DPP-IV inhibitors as a therapeutic modality, tumor microenvironments differ in terms of the extracellular matrix molecular composition, rigidity, and activity of local metalloproteases, rendering the area inaccessible to the potential infiltration of NKT or activated T cells [202,203].