Lp-PLA2, a potential protector of lung cancer patients complicated with pleural effusion from lung diseases, proves effective for the diagnosis and pathological classification of lung cancer

•Lp-PLA2 may be a protective factor of lung cancer in patients complicated with pleural effusion of lung diseases.•Lp-PLA2 can be used pathological classification of lung cancer.•Among lung cancer patients, the higher the concentration of serum Lp-PLA2, the lower the probability of squamous cell carcinoma, the higher the probability of adenocarcinoma.•Serum Lp-PLA2 concentration was not correlated with TNM stages of lung cancer.