SPP1 and lung cancer: Of the 22 upregulated DGEs, DDIT4 [47, 48], FAT1 [49, 50], HSPB1 [51, 52], ZIC2, and SPP1, most among these genes defined as hub genes, are broadly expressed in the nervous system and tumor tissues, and may examine the functional contribution during neuronal differentiation, neuronal death, as well as correlate with malignant biological behaviors of lung cancer.