What does fluid on/in the lung mean? by winfrith49 » Fri Jan 13, 2012 5:46 pm. Fluid on the lungs cannot be a definite diagnosis for lung cancer...you'll have to have the fluid biopsied and tested...if malignant(cancerous) cells are found, then it'd be lung cancer. However, fluid on the lungs can also mean infection (pneumonia or TB or something else), pancreatitis and other conditions. So, I can;t say for sure that you have cancer what would lead to the diagnosis of your condition is a biopsy.