Mesothelioma in the chest

Your chest lining has two layers. The inner layer lines your lung, and the outer layer lines your chest wall. The space between the two layers contains a small amount of fluid. This lubricates the two surfaces and lets the lung and chest wall move and expand as you breathe. When a tumour grows within the chest lining, it causes it to thicken at first. Then it spreads within the space between the layers. The tumour often produces fluid, sometimes several litres.