Lung Cancer

Lung cancer is a disease in which malignant (cancer) cells form in the tissues of the lung. It is the second most common cancer and the most common cause of cancer-related death in both men and women in the United States. There are two main types of lung cancer, small cell lung cancer and non-small cell lung cancer, based on how the cells look under a microscope. Non-small cell lung cancer can further be divided into a few subtypes, including

Squamous cell carcinoma: Cancer that begins in squamous cells, which are thin, flat cells that look like fish scales. This is also called epidermoid carcinoma.
Large cell carcinoma: Cancer that may begin in several types of large cells.
Adenocarcinoma: Cancer that begins in the cells that line the alveoli and make substances such as mucus.

Small cell lung cancer grows and spreads more quickly than non-small cell lung cancer.

Symptoms and Diagnosis

Sometimes lung cancer does not cause any symptoms and is found during a routine chest x-ray. The following symptoms may be caused by lung cancer or by other conditions:

A cough that doesn't go away.
Trouble breathing.
Chest discomfort.
Wheezing.
Streaks of blood in sputum (mucus coughed up from the lungs).
Hoarseness.
Loss of appetite.
Weight loss for no known reason.
Feeling very tired.

To diagnose lung cancer, the following tests and procedures may be used:

Physical exam and history.
Chest x-ray.
CT scan (CAT scan).
PET scan.
Sputum cytology: A procedure in which a pathologist views a sample of sputum (mucus coughed up from the lungs) under a microscope, to check for cancer cells.
Fine-needle aspiration biopsy of the lung: The removal of part of a lump, suspicious tissue, or fluid from the lung, using a thin needle. This procedure is also called needle biopsy. Ultrasound or another imaging procedure is used to locate the abnormal tissue or fluid in the lung. A small incision may be made in the skin where the biopsy needle is inserted into the abnormal tissue or fluid. A sample is removed with the needle and sent to the laboratory. A pathologist then views the sample under a microscope to look for cancer cells. A chest x-ray is done after the procedure to make sure no air is leaking from the lung.
Bronchoscopy: A procedure to look inside the trachea and large airways in the lung for abnormal areas. A bronchoscope (a thin, lighted tube) is inserted through the nose or mouth into the trachea and lungs. Tissue samples may be taken for biopsy.
Thoracoscopy: A surgical procedure to look at the organs inside the chest to check for abnormal areas. An incision (cut) is made between two ribs, and a thoracoscope (a thin, lighted tube) is inserted into the chest. Tissue samples and lymph nodes may be removed for biopsy. This procedure may be used to remove parts of the esophagus or lung. If certain tissues, organs, or lymph nodes can´t be reached, a thoracotomy may be done. In this procedure, a larger incision is made between the ribs and the chest is opened.
horacentesis: The removal of fluid from the space between the lining of the chest and the lung, using a needle. A pathologist views the fluid under a microscope to look for cancer cells.

Causes

All cancers are caused by dysfunctions of proteins involved in cell division, apoptosis, or DNA repair (see general characteristics). Dysfunctional proteins may arise from gene mutations or protein interactions with environments. The following risk factors may increase the chance of developing lung cancer (more info):

Smoking cigarettes or cigars, now or in the past.
Being exposed to second-hand smoke.
Being treated with radiation therapy to the breast or chest.
Being exposed to asbestos, radon, chromium, arsenic, soot, or tar.
Living where there is air pollution.

Reference:

National Cancer Institute, USA.