<qa>  What is the goal of the study?This is a phase II, placebo-controlled, randomized, double-blinded clinical trial. Study objective is to assess the efficacy and safety of mirtazapine in advanced NSCLC patients with malignant tumor related depression. Study hypothesis is that advanced NSCLC diagnosed with depression undertaking palliative chemotherapy with mirtazapine treatment for 8 weeks will have remarkable improvement in depression compared to baseline. Palliative chemotherapy and mirtazapine have better efficacy, recovery rate, response duration, tolerance and quality of life improvement than palliative chemotherapy and placebo. Moreover, mirtazapine could improve patients anxiety and chemotherapy related nausea and vomit. 