PLAU and gastric cancer: A large number of studies have shown that many proteases, such as urokinase-type plasminogen activator (uPA) and matrix metalloproteinase (MMP) [22,23,24], are upregulated in various tumors, including breast cancer, gastric cancer, ovarian cancer, colorectal cancer and other types of tumors [25], which helps to promote the growth and metastasis of tumor cells.