The presence of pleural effusion in ovarian cancer is considered to be related to further development of the disease, which may be caused by factors such as hypoproteinemia, distant metastasis and local inflammation. 1. Hypoproteinemia: ovarian cancer belongs to malignant tumors, with the development of the disease, patients may suffer from hypoproteinemia due to consumption, and plasma colloid osmotic pressure will be lowered, resulting in pleural effusion. 2. Distant metastasis: ovarian cancer has the characteristics of easy recurrence and proliferation. When ovarian cancer has metastasis and proliferation in diaphragm and pleura, it will destroy local capillaries, leading to liquid generation and red blood cell exposure, and then pleural effusion symptoms will appear. 3. Local inflammatory stimulation: ovarian cancer is malignant disease, tumor cells may cause local inflammatory reaction, which will promote the increase of permeability of pleural capillaries, resulting in the continuous infiltration of intravascular components into pleural cavity and the formation of pleural effusion. Excessive pleural effusion can compress the lung tissue and cause dyspnea. In the case of pleural effusion on the left side, it may even affect the heart beat. For patients with pleural effusion, if cancer cells are found in the effusion, they can be directly diagnosed as stage IV ovarian cancer, which is the most advanced stage. After ovarian cancer develops pleural effusion, patients should actively cooperate with doctors to improve their prognosis.