DPP4 and neoplasm: DOX significantly suppressed tumor growth in both control and DPP-4-kd 4T1 tumors, but DOX-mediated suppression was less trend in DPP-4-kd 4T1 tumors (Figure 5A; weight suppression rate (%) by DOX: control 42.8% vs. DPP-4-kd 29.7%).