PURPOSE: L ife expectancy of cancer patients determine the regimen of treatment. There is no feasible marker that determines the survival other than the stage of the disease or other patients related factors. Bilirubin can be a revealing marker for these. The effect of bilirubin may be due to the fact that the genetic and biochemical processes of bilirubin also modulate the tumour microenvironment. Radiotherapy and bilirubin can produce an effect similar to metformin via AMPK pathway. MATERIALS AND METHODS: This analysis was performed retrospectively in a cohort of 80 patients with a diagnosis of locoregional lung cancer with bilirubin levels in the accepted range. Receiver operating characteristic curve (ROC) analysis was performed to determine the optimal cut-off points. Pre-treatment serum total bilirubin (TBIL), direct bilirubin (DBIL), indirect bilirubin (IBIL) levels and tumour volumes in the prognosis of the patients were investigated. RESULTS: The cut-off points for serum TBIL, DBIL and IBIL were 0.565 mg/dL, 0.105 mg/dL and 0.415 mg/dL, respectively. High TBIL 47.5 %, high DBIL and high IBIL were observed in 45 % of the entire patient population. The overall survival was three times longer in the high TBIL group than in the low TBIL group (OS; Hazard Ratio (HR), 0.33; 95% CI 0.16-0.70; p < 0.001), locoregional free survival (LRFS; HR, 0.44; 95% CI 0.27-0.71; p <0.001) and distant metastasis-free survival (DMFS; HR, 0.44; 95% 0.25-0.80; p < 0.001). Similarly, high DBIL and high IBIL levels have been associated with longer OS, LRFS, and DMFS with signifi cant differences. In addition, in the survival analysis of the cohort stratifi ed with gross tumour volume (GTV) 128.5cc and TBIL 0.565 cut-off values; In the comparison of high TBIL and low TBIL groups, a signifi cantly longer OS was observed in the high TBIL group in the patients with a GTV volume greater than128.5cc (p <0.001). CONCLUSION: Plasma bilirubin level at the time of diagnosis affects the survival of the patients independent of cancer stage and tumour volume. Possible additive interactions of radiotherapy and bilirubin are discussed with their pathophysiological mechanisms (Tab. 2, Fig. 7, Ref. 26).