Lung cancer is a disease that begins in the lungs. Lungs are part of the respiratory system that works together to help you breathe. The respiratory system’s main function is to move fresh air into your body while removing waste gases. Lung cancer occurs when there is an uncontrolled growth of abnormal cells in the lung which can interfere with normal lung function. The abnormal cells can pass from the original part of the lung to other parts of the body, such as the opposite lung, our lymph nodes, bones, liver and more.