EGFR and Pleural effusion: Among all patients, univariate analyses showed that the EGFR mutation rate was significantly higher in females (P < 0.001), without a smoking history (P < 0.001), non‐squamous (P < 0.001), stage IV tumor (P < 0.001), bone metastases (P = 0.014), brain metastases (P = 0.002), pleural effusion (P = 0.016) and pleural nodules (P = 0.014) (Table 3).