Bouin staining of the lung revealed that DPP-4-kd 4T1 tumor-bearing mice exhibited more lung metastasis when compared to control mice with or without DOX; DOX treatment in both control and DPP-4-kd 4T1 tumor-bearing mice displayed some trend of induction in lung metastasis due to an extremely higher incidence of lung nodules in some mice (Figure 5C). This evidence concerns the gene DPP4 and neoplasm.