When cancer cells are found in the pleural fluid and the primary lesion itself belongs to lung cancer, it belongs to relatively advanced stage and needs to be controlled by radiotherapy. In the early stage, the primary tumor in the lung is only confined to the lung, and even if there is pleural effusion, it is not accompanied by tumor cells; once cancer cells are found in the pleural fluid, it means that pleural metastasis has begun to occur, and the corresponding condition suggests that the tumor has entered into the advanced stage, which can not be completely cured by surgical resection, and it needs to be controlled through auxiliary methods, and it is important to pay attention to standardized treatment under the guidance of the clinicians. After the emergence of the corresponding condition, it is necessary to diagnose the cytopathological condition, administer drugs regularly according to the specific tumor typing, and if necessary, do the genotype determination, and target therapy can be done if there is a gene mutation.