It is hypothesized that CTSG is a protective factor in the development of non-small cell lung cancer and HIV-related lung cancer, delaying the immune damage caused by HIV virus to the organism and the development of lung cancer; low expression of CTSG protein promotes the development of non-small cell lung cancer and HIV-related lung cancer, which may suggest that patients have a poor prognosis. The gene discussed is CTSG; the disease is lung cancer.