Statistical analysis With the purpose of description, the continuous variables will be expressed as arithmetic means, medians, and Standard deviations (SDs), the variable categories as proportions and 95% confidence intervals (95% CIs). Inferential comparisons will be conducted by means of the Student t test or the Mann-Whitney U test according to data distribution (normal and non-normal, respectively) determined by the Kolmogorov-Smirnov test, for example, comparison of age means between both groups. The X2 test or the Fisher exact test will be employed to evaluate significance among categorical variables, for example, both groups (atRA vs. placebo) of ECOG higher or lower than 80, stage IIIB vs. IV, history of smoking, RAR expression, and response. Statistical significance will be determined as a p value (p <0.05) with a two-tailed test. PFS and GS times will be determined from day of initiation of chemotherapy until date of death, respectively, and will be analyzed by the Kaplan-Meier test. Comparisons between groups will be performed with the log-rank test. All variables were dichotomized analyses of the survival curves. Adjustment for potential confounders will be performed by means of Cox proportion multivariate regression analysis. The SPSS version 15 (SPSS, Inc., Chicago, IL, USA) software package will be used for data analysis.