Stage IV lung cancer: In contrast to the early stages of lung cancer, the disease at this stage has spread to other parts of the body. Tumors in the lungs can be of any size and may (but not necessarily) have spread to distant lymph nodes. Stage IV is subdivided into stage IVA and stage IVB.

Tumors in stage IVA have spread either from one lung to the other or extensively within the thoracic cavity, forming secondary tumors locally, or to the pericardial sac (forming secondary tumors there as well) or to the fluid surrounding the lungs (pleural fluid) or around the heart (pericardial fluid). Also, tumors at this stage may have invaded an area outside the thoracic cavity, such as an adrenal gland or a bone.

Tumors in stage IVB have spread to multiple organs outside the thoracic cavity.