A cytology exam of pleural fluid is a laboratory test to detect cancer cells and certain other cells in the area that surrounds the lungs. This area is called the pleural space. Cytology means the study of cells. In an abnormal test, there are cancerous (malignant) cells. This may mean there is a cancerous tumor. A cytology exam is used to look for cancer and precancerous cells. It may also be done for other conditions, such as identifying systemic lupus erythematosus cells. If you have signs of fluid buildup in the pleural space, this condition is called pleural effusion. The test may also be done if you have signs of lung cancer. This test most often detects: Breast cancer, lymphoma, lung cancer, ovarian cancer, and stomach cancer, helping in the diagnosis and management of these conditions.