Conversely, studies have also shown that DPP9 expression is reduced in human oral squamous cell carcinoma (OSCC), knockout of DPP9 in tumor cells accelerates cell proliferation, while overexpression of DPP9 inhibits tumor cell proliferation, invasion, metastasis, and epithelial-mesenchymal transition (Wu et al., 2020). The gene discussed is DPP9; the disease is oral cavity squamous cell carcinoma.