In this study, we aimed to investigate the diagnostic and prognostic roles and the effects of chemotherapy of serum proinflammatory cytokines consisting of IL-6, TNF-alpha, CRP, and leptin levels in patients with advanced-stage non-small cell lung cancer. Twenty-eight patients newly diagnosed of non-surgical advanced non-small cell lung cancer and 15 healthy controls were included. All patients with good performance status were treated with combination therapy consisting of cisplatin plus vinorelbine chemotherapy. Blood samples were obtained in fasting conditions before chemotherapy first and after two cycles of chemotherapy. IL-6 and TNF-alpha immunoassays employ the quantitative sandwich enzyme immunoassay technique. Leptin (Sandwich) ELISA is a solid-phase enzyme-linked immunosorbent assay based on the sandwich principle. CRP is a photometric immunoturbidimetric test. Most of the patients were elderly, male predominance, good performance status, and no or less than 10% weight loss. Higher serum TNF-alpha (p < 0.001) and CRP (p < 0.001), and lower leptin (p = 0.021) levels in patients than in controls. Serum IL-6 cytokine (p = 0.693) levels were not significantly different. No statistically significant relationships between investigated serum parameters and various characteristics of patient and disease. Likewise, serum levels of leptin, IL-6, TNF-alpha, and CRP were all similar in lung cancer patients independently from severity of weight loss (p > 0.05). A direct relationship was found between serum IL-6 and TNF-alpha levels (r = 0.530, p = 0.004). We found that both serum leptin (p = 0.046) and IL-6 (p = 0.002) levels were decreased owing to the chemotherapy effect independently from chemotherapy response. However, serum TNF-alpha and CRP levels were not changed by the chemotherapy effect. The stage of the disease, serum LDH levels, performance status, and responsiveness to chemotherapy yielded prognostic value. Only serum IL-6 levels out of the parameters showed a trend (p = 0.06) related to a worse prognosis.