To explore the role that the cysteine cathepsin family plays in lung cancer pathogenesis, we investigated The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets and compared the gene expression of cathepsins family (CTSB, CTSC, CTSF, CTSH, CTSK, CTSL, CTSO, CTSS, CTSV, CTSW and CTSX) changes in lung cancer tissues and normal tissues. The gene discussed is CTSO; the disease is lung cancer.