SPP1 and neoplasm: OPN level was related to disease stage (P = 0.012), tumor size (P = 0.034), and lymph node metastasis (P = 0.037), while there were no difference with age (P = 0.954), gender (P = 0.317), smoking status (P = 0.077), performance status (P = 0.174), and chemotherapy responses (P = 0.485, Table 2).