SOX9 and lung cancer: Our results also revealed that SOX9 expression was significantly associated with age, tumor size, histological differentiation, tumor stage, lymph node metastasis and TNM stage, which had the same results in other malignant tumors, such as hepatocellular carcinoma, breast cancer, prostate cancer, lung cancer, esophageal cancer and colorectal cancer.[21,52,57–60] Therefore, it was widely known that SOX9 is able to promote tumor cell proliferation, invasion and metastasis.