In approximately 25% of people with lung cancer, there are no symptoms and the cancer is detected during screening or a routine physical examination. However, in three-quarters of lung cancer patients there are warning symptoms and signs that can alert the patient or their physician.

Most commonly, lung cancer patients experience respiratory symptoms such as shortness of breath, wheezing, hoarseness and a persistent cough. These symptoms are very common among smokers, and are also present in a number of other conditions such as asthma, emphysema and chest infections. A new cough should always be evaluated, as it may be a symptom of lung cancer. Lung cancer may spread to the chest wall, causing chest, shoulder and back pain. If cancer cells erode lung blood vessels, the patient may cough up blood. There may also be other generalized effects that occur with most cancers, such as fever, fatigue, appetite loss and weight loss.

As a lung cancer grows, it increasingly compromises the normal functioning of an affected lung. Secondary complications may occur, such as collection of fluid in the tissue lining the lungs (pleural effusion), lung collapse, airway obstruction, and repeated lung infections. Lung cancer may also spread or metastasize to other parts of the body such as the lymph nodes, bones, liver and brain. Bone pain and abnormal liver or brain function may result.

The absence of symptoms does not necessarily indicate early disease, and the presence of non-specific chest symptoms can often go unheeded. Both these factors contribute to the fact that only about 15 percent of lung cancer patients are diagnosed in the early stages of disease. The later lung cancer is diagnosed, the less effective treatment options are. Delays in diagnosing lung cancer patients result in an overall survival rate of only 15 percent at five years after diagnosis.