Furthermore, overexpression of CDK4 has been observed in many tumor types, including oral squamous cell carcinoma [6], pancreatic endocrine tumors [7], lung cancer [8,9], and nasopharyngeal carcinoma [10], suggesting that CDK4 is a significant factor in promoting the initiation and development of tumors. This evidence concerns the gene CDK4 and pancreatic neuroendocrine tumor.