What is stage I, II, III or IV lung cancer?

The stage of a cancer describes the extent of the cancer. It is based on the size and location of the tumor, and whether it has spread to the lymph nodes or other parts of the body. A stage 1 lung cancer is located only in the lungs and has not spread to any of the lymph nodes. A stage 2 lung cancer is a bit more advanced, where the cancer has spread to the localized lymph nodes. A stage 3 cancer is one where the lymph nodes in the middle part of the chest are also involved (the area called the mediastinum). A stage 4 lung cancer is one that has spread outside the chest, either to the other lung, or to other parts of the body, such as the bone or brain or liver or adrenal glands.