The levels of TuM2-PK in pleural effusion and serum of SCLC were significantly higher than that of lung ADC and SCC (P < 0.01), while the level of TuM2-PK in pleural effusion and serum of lung ADC was also higher than that of lung SCC (P < 0.05); CEA increased most significantly in lung ADC, and its level was significantly higher in lung SCC and SCLC (P < 0.05) (Fig. 1A–D). This evidence concerns the gene CEACAM5 and Pleural effusion.