A case of gastric cancer detected incidentally following to chylothorax, followed by change in the appearance of pleural effusion with cancer progression.

We report a case of gastric cancer that was detected due to chylothorax. A 64-year-old man visited our hospital with chief complaints of anterior chest pain and right lower leg swelling. Chest X-ray showed bilateral pleural effusion. Biochemical tests of the pleural fluid detected chyle and cytological examination of the left pleural revealed poorly differentiated adenocarcinoma cells. An upper gastrointestinal examination revealed a type 4 gastric cancer that was diagnosed as the primary lesion. The appearance of the pleural effusion changed from chylaus to light yellow as the cancer progressed. Gastric cancer combined with chylothorax is quite rare and we discussed in this report how this change of the appearance of the pleural effusion occurred in comparison with the mechanism of chylothorax.