Both squamous lung cancer and adenocarcinoma of the lung can cause pleural effusion, and adenocarcinoma of the lung has more chances to cause pleural effusion. Squamous lung cancer is mostly seen in central type lung cancer, which easily causes obstructive pneumonia, pulmonary atelectasis, irritating dry cough, blood in sputum, repeated infections causing high fever and chest pain, etc. Peripheral type lung cancer is mostly adenocarcinoma, which is prone to pleural metastasis and formation of pleural effusion. Therefore, both squamous lung cancer and adenocarcinoma of the lung can cause pleural effusion, and adenocarcinoma has more chances. Other breast cancer, thyroid cancer, nasopharyngeal cancer and gynecologic choriocarcinoma are also prone to cause pleural effusion when bilateral lung metastasis occurs. Especially ovarian cancer with lung metastasis is likely to cause a large amount of pleural effusion. During the examination, it is necessary to clarify the primary lesion and not to misdiagnose it as bronchopulmonary cancer, and it is necessary to check whether the pleural effusion is caused by the metastasis of gynecologic cancer to the lung.