Stage I non-small cell lung cancer is divided into stages IA and IB. In stage IB, cancer has not spread to the lymph nodes and one or more of the following is true: (1) the tumor is larger than 3 centimeters but not larger than 5 centimeters; (2) cancer has spread to the main bronchus and is at least 2 centimeters below where the trachea joins the bronchus; (3) cancer has spread to the innermost layer of the membrane that covers the lung; and/or (4) part of the lung has collapsed or become inflamed.