(A–C) MUC5AC protein levels were analyzed immunohistochemically using human tissue arrays. Representative images of MUC5AC immunostaining in adenocarcinoma (ADC) (A) and squamous cell carcinoma (SCC) (B) are shown. Scale bars: 200 μm (low magnification) and 10 μm (high magnification). (C) MUC5AC H-scores for ADC (n = 53) and adenosquamous (n = 3) (combined and included with ADC, red circles) were compared with SCC (n = 21, gray circles). MUC5AC levels were significantly higher in ADC tissues. Data are individual values with lines depicting medians ± 95% CIs. Significance was determined by the Wilcoxon rank sum test (61). P < 0.05. (D–F) Effects of MUC5AC expression on survival in ADC and SCC were tested using KM Plotter (http://kmplot.com/analysis/). MUC5AC expression was stratified to define high- (red) and low-expression (black) groups by median transcript levels. Kaplan-Meier survival plot and hazard ratio calculations were compared by multivariate log-rank analyses with sex and stage as covariates; P < 0.05. While sex was not significant, stage was strongly significant for ADC (log-rank P < 1 × 10–14). Significant effects of high MUC5AC gene expression were observed for all human lung ADC (D, n = 534, log-rank P < 0.0001) and for stage I ADC (E, n = 370, log-rank P = 0.001) samples. No differences were observed in SCC (F, n = 315, log-rank P = 0.62). For all groups in D–F, calculated hazard ratios were 2.0 (1.5–2.7) for all ADC, 1.9 (1.3–2.8) for stage I ADC, and 1.1 (0.8–1.5) for SCC.