Membrane-bound dipeptidyl peptidase 5 (DPP5) has been linked to tumor invasion and metastasis processes. Its recent isolation as a soluble protein from plasma may indicate a potential role as a biomarker and prognostic factor for tumors, and as a potential therapeutic target.

DPP5 and DPP4 levels are reproducible parameters to correlate with disease status, with lower levels noted in cancer patients compared with healthy subjects; but higher levels in metastatic cancers compared with non-metastatic cancers. These findings support a prognostic role for plasma DPP5 and DPP4 levels and they should be considered in attempts to use DPP5 as a therapeutic target to hinder cancer progression. An explanation of low levels of plasma DPP5 in cancer despite previously-reported high level of local expression remains to be determined.