Lung cancer, also known as lung carcinoma, is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung.  If left untreated, this growth can spread beyond the lung by the process of metastasis into nearby tissue or other parts of the body.Most cancers that start in the lung, known as primary lung cancers, are carcinomas.  The two main types are small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (NSCLC).The most common symptoms are coughing (including coughing up blood), weight loss, shortness of breath, and chest pains.

SYMPTOMS :-

A new cough in a smoker or a former smoker should raise concern for lung cancer.

A cough that does not go away or gets worse over time should be evaluated by a health-care professional.

Coughing up blood (hemoptysis) occurs in a significant number of people who have lung cancer. Any amount of coughed-up blood is cause for concern.

Chest pain is a symptom in about one-fourth of people with lung cancer. The pain is dull, aching, and persistent.

Shortness of breath usually results from a blockage to the flow of air in part of the lung, collection of fluid around the lung (pleural effusion), or the spread of tumor throughout the lungs.

Wheezing or hoarseness may signal blockage or inflammation in the lungs that may go along with cancer.

Repeated respiratory infections, such as bronchitis or pneumonia, can be a sign of lung cancer.

Symptoms of metastatic lung tumors depend on the location and size. About 30% to 40% of people with lung cancer have some symptoms or signs of metastatic disease.

Lung cancer most often spreads to the liver, the adrenal glands, the bones, and the brain.
Metastatic lung cancer in the liver may cause a loss of appetite, feeling full early on while eating, and otherwise unexplained weight loss.
Metastatic lung cancer in the adrenal glands also typically causes no symptoms.

Metastasis to the bones is most common with small cell cancers but also occurs with other lung cancer types. Lung cancer that has metastasized to the bone causes bone pain, usually in the backbone (vertebrae), the large bones of the thigh (the femurs), the pelvic bones, and the ribs.

CAUSES:-
Cigarette smoking is the most important cause of lung cancer.

Passive smoking, or secondhand smoke, presents another risk for lung cancer.

Air pollution from motor vehicles, factories, and other sources probably increase the risk for lung cancer, and many experts believe that prolonged exposure to polluted air is similar to prolonged exposure to passive smoking in terms of risk for developing lung cancer.

Asbestos exposure increases the risk of lung cancer nine times. A combination of asbestos exposure and cigarette smoking raises the risk to as much as 50 times. Another cancer known as mesothelioma (a type of cancer of the inner lining of the chest cavity and the outer lining of the lung called the pleura, or of the lining of the abdominal cavity called the peritoneum) is also strongly associated with exposure to asbestos.

Lung diseases, such as tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), also create a risk for lung cancer. A person with COPD has a four to six times greater risk of lung cancer even when the effect of cigarette smoking is excluded.

Radon exposure poses another risk.
Radon is a byproduct of naturally occurring radium, which is a product of uranium.
Radon is present in indoor and outdoor air.

Certain occupations where exposure to arsenic, chromium, nickel, aromatic hydrocarbons, and ethers occurs may increase the risk of lung cancer.