Spontaneous pneumothorax (SP) is a rare manifestation of lung cancers, especially as the first sign. The mechanism producing pneumothorax from pulmonary cancer has three main reasons, One is that the cancer necrosis directly ruptured into the pleural space. Another is that endobronchial neoplasm acts as a check valve, leading to dilation and eventual rupture of distal alveolar spaces. The third is that the rupture of small subpleural blebs accidentally causes SP. However, the prognosis of lung cancer patients with initial manifestation of SP is very poor, SP seems to be an ominous sign for the primary cavity lung cancer patients, even in an early stage.