According to the results obtained from the TIMER database, the PLK4 expression was significantly higher in uroepithelial carcinoma of the bladder, invasive breast cancer, squamous, and adenocarcinoma of the cervix, bile duct cancer, colon cancer, esophageal cancer, squamous cell carcinoma of the head and neck, renal suspicious cell carcinoma, renal clear cell carcinoma, renal papillary cell carcinoma, gastric cancer, thyroid cancer, and endometrial cancer, than in normal tissue (Figure 1(a)). Here, PLK4 is linked to bile duct cancer.