Most cancer researchers believe that 20 or more years pass from the time that a person starts to inhale a cancer-producing substance, such as tobacco smoke, and the time cancer actually develops.
Lung cancer is very difficult to detect at an early stage. Because of the large size of the lungs, cancer may grow for many years without any symptoms. Symptoms of lung cancer (e.g., persistent cough, etc.) do not always appear in the early stages of lung cancer. Even then, a persistent cough may be diagnosed as bronchitis and treated with antibiotics.
Unlike some other cancers, there is no universally accepted screening test for lung cancer. It is known that chest x-rays and CT scans can detect small tumours. However, these types of tests are usually ordered after the patient has developed symptoms. IN some cases, lung cancer is found during a routine check-up.