Lung cancer was unidentified as a disease until mid 1700. The history states the possible sightings of lung cancer during early cavemen on the basis of archaeological findings. The oldest documented cases of cancer was recorded on papyrus in 1500 BC.
Tumors of the lung may be benign or malignant. A malignant chest tumor can be primary, arising within the lung, chest wall, or mediastinum or it can be a metastasis from primary tumor site elsewhere in the body.
Lung cancer is the leading cancer killer among men and women. It is estimated 31% of cancer deaths in men and 26% in women are related to lung or Bronchus cancers. Approximately 213,000 new cases of lung cancer are diagnosed annually; 15% of new cancers for men and women involve the lung or bronchus. Almost 70% of patients with lung cancer, the disease has spread to regional lymphatics and other sites by the time of diagnosis. As a result, the lung term survival rate is low. Overall, the 5-year survival rate is 16%.
The most common cause of lung cancer is inhaled carcinogens, most often cigarette smoke (90%); other carcinogens include radon gas and occupational and environmental agents. Lung cancers arise from a single transformed epithelial cell in the tracheobronchial airway, in which the carcinogens binds to and damages the cell’s DNA. This damage results in cellular changes, abnormal cell growth, and eventually a malignant cell. As the damaged DNA is passed on to daughter cells, the DNA undergoes further changes, the pulmonary epithelium undergoes malignant transformation from normal epithelium to invasive carcinoma. Carcinoma tends to arise at sites of previous scarring (TB, fibrosis) in the lung.
Classification and staging
Most lung cancers are classified into one of two major categories:
- Small cell carcinoma represents 15% to 20% of tumors. Most small cell cancers arise in major bronchi and spread by infiltration along the bronchial wall.
- Non-small cell lung carcinoma (NSCLC) represents approximately 80% of tumors. The cell types include squamous cell carcinoma (20% to 30%), which is usually more centrally located, large cell carcinoma (15%) which is fast growing and tends to arise peripherally; and adenocarcinoma (40%), which presents as peripheral masses and often metastasizes and including bronchoalveolar carcinoma which is the most prevalent carcinoma of the lung in both men and women.
In addition to classification according to cell type, lung cancer are staged. The stage of the tumor refers to the size of the tumor, its location, whether lymph nodes are involved, and whether the cancer has spread. Small cell lung cancers are classified as limited or extensive.
Various risk factors have been associated with the development of lung cancer, including smoking tobacco, second-hand (passive) smoke, environmental and occupational exposures, gender, genetics, and dietary deficits. Other factors that have been associated with lung cancer include genetic predisposition and underlying respiratory disease such as COPD (chronic obstructive pulmonary disease) and TB.
Tobacco use is responsible for more than one of every six deaths from pulmonary and Cardiovascular diseases. Lung cancer is 10 times more common in cigarette smokers than non smokers. Risk is determined by the pack-year history (number of packs of cigarettes used each day, multiplied by numbers of years smoked), the age of initiation of smoking, the depth of inhalation and the tar and nicotine levels in the cigarettes smoked. The younger person is when he or she starts smoking, the greater the risk of developing lung cancer.
Cigarette smoke contains over 4,000 chemicals including 43 known cancer causing (carcinogenic) compound and other 400 toxins. Its ingredients include nicotine which is highly addictive and it reaches to your brain in just 6 seconds, tar, and carbon monoxide as well as formaldehyde, ammonia, hydrogen, cyanide, arsenic and DDT.
Passive smoking has been identified as a possible cause of lung cancer in non-smokers. It is estimated that second-hand smoke causes about 3000 deaths per year. People who are involuntarily exposed to tobacco smoke in a closed environment (house, automobiles, building) have an increased risk of lung Cancer when compared with unexposed non-smokers.
Environmental and occupational exposure
Various carcinogens have been identified in the atmosphere, including motor vehicle emissions and pollutants from refineries and manufacturing plants. Evidence suggests that the incidence of lung cancer is higher in urban areas as a result of the build-up of pollutants and motor vehicle emissions.
Radon is a colourless, odourless gas found in soil and rocks. High levels of radon have been associated with the development of lung cancer, especially when combined with cigarette smoking. Homeowners are advised to have radon levels checked in their houses and to arrange for special venting if the levels are too high.
Chronic exposure to industrial carcinogens such as arsenic, asbestos, mustard gas, chromates, coke oven fumes, nickel, oil and radiation has been linked with development of lung cancer. Several laws have been passed to control exposure to these carcinogens in the workplace.
Some familial predisposition to lung cancer seems apparent because the incidence of lung cancer in close relatives of patients with lung cancer appears to be two to three times that in the general population regardless of smoking status.