Lung: The lungs are the body's major organs of respiration. The two vital parts that make up the lungs are located on each side of the chest within the rib cage. Each lung is divided into upper and lower lobes, although the upper lobe of the right lung contains another triangular subdivision known as the middle lobe. The bottom, or base, of each lung extends down to the diaphragm, which is the major breathing-associated muscle that separates the chest from the abdominal cavity.

The right lung is larger and heavier than the left lung, which is somewhat smaller in size because of the position of the heart.

The lung parenchyma is made up of clusters of spongy air sacs called lobules. There are about 130,000 primary lobules in each lung. Each lobule is approximately 3.5 millimeters in diameter and contains about 2,200 alveoli (air sacs and ducts) which keep them from collapsing during breathing.

Epidemiology

• Lung cancer is the second most common cancer among both men and women and is the leading cause of cancer death for both.
• Men: Rates (per 100,000) range from a low of about 14 among American Indians to a high of 117 among African Americans.
• Women: Narrower range, from a rate of about 15 among Japanese to nearly 51 among Alaska Natives
• In the 30-54 year age group, incidence rates among men are double those among women in most of the racial/ethnic groups.
• Filipino men have an incidence rate nearly twice as large as their mortality rate.
• More Americans die each year from lung cancer than from breast, prostate, and colorectal cancers combined.
• Approximately 173,770 new cases of lung cancer will be diagnosed in 20043, accounting for 13% of all new cancer cases.
• An estimated 160,440 Americans will die in 2004 from lung cancer, accounting for 28% of all cancer deaths.

Risk Factors

• Diets low in fruits and vegetables may cause lung cancer.
• Risk increases after the age of 45 and increases more dramatically after the age of 65.
• Cigarette smoking accounts for nearly 90% of all lung cancers. Smokers or former smokers with a 30-pack-year or greater history are at risk of lung cancer.
• Pack year is the number of years someone has smoked multiplied by the number of packs smoked per day.
• Example: A person with a 30-pack-year history will have smoked one pack of cigarettes per day for 30 years or three packs per day for 10 years.
• Cigar smoking and pipe smoking also cause lung cancer.
• Smoking “low tar” cigarettes does not reduce the risk of lung cancer.
• Marijuana contains more tar than cigarettes, and the smoke is held in the lungs for a longer time. Marijuana is difficult to study because it is an illegal substance and many marijuana smokers also smoke cigarettes.
• Women smokers may have a higher risk of lung cancer than male smokers.
• Passive smoking also contributes to the development of lung cancer among non-smokers.
• Occupational exposures to asbestos and radon are linked with lung cancer.
• Asbestos workers have a seven times greater risk of developing the disease.
• Asbestos workers who smoke have a 50-90 times greater risk developing the disease.
• Air pollution also is a cause (small factor in incidence and mortality).
• Lung cancer is a disease of older people. Lung cancer is fairly rare in people under 40.
• If one stops smoking before lung cancer develops, damaged lung tissue gradually will return to normal.
• Ten years after quitting, the risk is reduced to one-third of what it was previously.

Prevention and Screening
There is no widespread screening test for lung cancer. At this time, the use of spiral CT scans are being studied for screening. Eighty percent of lung cancers can be prevented by avoiding tobacco use.

Click here to review the Surgeon General's Tobacco Cessation Guidelines.