MSFinals-2234

A 54-year-old woman presents to the medical admissions unit with complaints of breathlessness. Her GP had noted reduced breath sounds and dullness to percussion at the left lung base. An urgent chest X-ray reveals a left-sided pleural effusion. To identify the cause of the effusion, an aspirate of the pleural fluid is taken, and the results show a pleural effusion fluid protein/serum protein ratio of 0.73. What is the probable reason for the pleural effusion?