ISG15 and squamous cell lung carcinoma: Given that patients with lung adenocarcinoma had a 3.206-fold greater risk of death (95% CI: 1.293–7.947) than patients with squamous cell lung carcinoma, we performed an additional analysis to evaluate the prognostic significance of SIRT1, ISG15, and SIRT1/ISG15 expression in patients with squamous cell lung carcinoma and lung adenocarcinoma.