Content Summary : The lungs are vital organs. Working with the heart and circulatory system, they provide life-sustaining oxygen and rid the body of carbon dioxide. Normal lungs have a great reserve capacity to meet the body’s need for oxygen across a wide variety of circumstances. The same is true of the heart and circulatory system. This reserve capacity permits cancerous lung tumors to grow for years without compromising lung function. Furthermore, the lungs do not have many nerves to transmit pain messages. Therefore, a cancerous lung tumor can grow for many years without causing any symptoms. Unfortunately, this means that most people are not diagnosed with lung cancer until late in the disease process. Even more unfortunate is the fact that this long period of silent growth gives the cancer time to spread before it is diagnosed. Lung cancer that has spread beyond the original tumor is difficult to cure. Eventually, people with lung cancer do develop symptoms. Approximately 95% of people diagnosed with lung cancer have symptoms related to the disease. However, they occur late in the cancerous process. The long silent growth period of lung cancer has led to great interest in lung cancer screening, especially in recent years.