• Clinical Oncology Department, Faculty of Medicine, Ain Shams University , Cairo , Egypt.

Objectives: The current study aims to evaluate the correlation between pre-diagnostic body mass index (BMI) as well as BMI trajectory in relation to lung cancer development and mortality risks. Methods: This analysis is based on Prostate, Lung, Colorectal, and Ovary (PLCO) trial datasets. Based on 145544 participants with complete information about pre-diagnostic BMI/BMI trajectory, associations of BMI measurements during adult life (at 20 years, 50 years and at enrolment into the study) with lung cancer development and mortality risks were determined. Multivariate Cox regression models were used to determine hazard ratios (HRs) of lung cancer development and mortality risks. Results: Higher BMI at 20 years, 50 years as well as the time of enrolment was associated with lower probability of lung cancer development (P = 0.004; P < 0.001; P < 0.001; respectively). Among different BMI trajectories, lung cancer risk was decreased among patients who had normal BMI at age 20 then became overweight (P < 0.001) or obese (P < 0.001) at the age of 50 compared to patients who maintained normal BMI. Likewise, death from lung cancer was reduced among patients with higher BMI at 20 years, 50 years as well as at the time of enrolment (P = 0.027; P < 0.001; P < 0.001). Additionally, death from lung cancer was reduced among patients who had normal BMI at age 20 then became overweight (P < 0.001) or obese (P < 0.001) at the age of 50 compared to patients who maintained normal BMI. Conclusions: Overall, higher pre-diagnostic BMI seems to be associated with lower probability of lung cancer development and death. Moreover, an escalating temporal trajectory of pre-diagnostic BMI seems to be associated with a lower risk of the development of and death from lung cancer.