Types and Causes of Lung Cancer

Cancer occurs when normal cells undergo a transformation that causes them to grow and multiply without control. The cells form a mass or tumor that differs from the surrounding tissues from which it arises. Tumors are dangerous because they take oxygen, nutrients and space from healthy cells and because they invade and destroy or reduce the ability of normal tissues to function.

There are two major types of primary lung cancer: non-small cell and small-cell. Each affects different types of cells in the lung, and each grows and spreads in different ways. As such, treatments for these two types of primary lung cancer vary. A diagnosis will include not only the type of lung cancer but the stage - a term that is used to describe the extent and spread of the disease at the time of diagnosis. Tumors found in the lungs sometimes originate from cancers elsewhere in the body. These tumors are called lung metastases.

 (If the cancer has features of both types, it is called mixed small cell/large cell cancer. This is not common.)

Other Types of Lung Cancer

Along with the two main types of lung cancer, other tumors can be found in the lungs, too. Some of these are not cancer and others are cancer. Carcinoid tumors are an uncommon type of lung cancer, they are slow-growing and usually cured by surgery.

Keep in mind that cancer that starts in other organs (such as the breast, pancreas, kidney, or skin) can sometimes spread (metastasize) to the lungs, but these are not lung cancers. For example, cancer that starts in the kidney and spreads to the lungs is still kidney cancer, not lung cancer. Treatment for these cancers that have spread to the lungs depends on where the cancer started.

Small-Cell Lung Cancer (SCLC)

About 10 to15 percent of all lung cancers are the small-cell type. Other names for SCLC are oat cell carcinoma and small cell undifferentiated carcinoma. The primary cause of both small-cell and non-small-cell lung cancer is tobacco smoking. However, small-cell lung cancer is more strongly linked to smoking.

This cancer often starts in the bronchi near the center of the chest. Although the cancer cells are small, they can divide quickly, form large tumors and spread to lymph nodes and other organs throughout the body.

Surgery is rarely an option for this type of cancer and never the only treatment given. However, small-cell lung cancer responds well to chemotherapy and radiation therapy.

Non-Small Cell Lung Cancer (NSCLC)

Non-small cell lung cancer, the most common type of lung cancer, is usually associated with a history of smoking.  About nine out of ten cases of all lung cancers are the non-small cell type. There are three main sub-types of NSCLC. The cells in these sub-types differ in size, shape, and chemical make-up.

  • Squamous cell carcinoma: About 25 to 30 percent of all lung cancers are this kind. They are linked to smoking and tend to be found in the middle of the lungs, near a bronchus.
  • Adenocarcinoma: This type accounts for about 40 percent of lung cancers. It is usually found in the outer part of the lung. This type of lung cancer occurs mainly in people who smoke (or have smoked), but it is also the most common type of lung cancer seen in non-smokers. It is more common in women than in men, and it is more likely to occur in younger people than other types of lung cancer.
  • Large-cell (undifferentiated) carcinoma: About 10 to 15 percent of lung cancers are this type. It can start in any part of the lung. It tends to grow and spread quickly, which makes it harder to treat.

Non-small cell lung cancer is classified by one of four stages: stage I, in which the cancer is confined to the lung; stages II and III, in which the cancer is confined to the chest; and stage IV, in which the cancer has spread from the chest.


What Causes Non-Small Cell Lung Cancer?

A risk factor is anything that affects a person's chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, such as smoking, can be controlled. Others, like a person's age or family history, can't be changed.

But risk factors don't tell us everything. Having a risk factor, or even many risk factors, does not mean that you will get the disease. And some people who get the disease may not have had any known risk factors. Even if a person with lung cancer has a risk factor; it is often very hard to know how much that risk factor may have contributed to the cancer.

Still, several risk factors can make you more likely to develop lung cancer:

Tobacco Smoke

Smoking is by far the leading risk factor for lung cancer. Tobacco smoke causes nearly nine out of ten cases of lung cancer. The longer a person has been smoking and the more packs a day smoked, the greater the risk. If a person stops smoking before lung cancer starts, the lung tissue slowly repairs itself.

Cigar and pipe smoking are almost as likely to cause lung cancer as is cigarette smoking. Smoking low tar or "light" cigarettes increases the risk of lung cancer as much as regular cigarettes. There is concern that menthol cigarettes may increase the risk even more since the menthol allows smokers to inhale more deeply.

People who don't smoke but breathe the smoke of others may also be at a higher risk for lung cancer. Non-smokers who live with a smoker, for instance, have about a 20 to 30 percent greater risk of developing lung cancer. Non-smokers exposed to tobacco smoke in the workplace are also more likely to get lung cancer.

Stopping smoking at any age may lower the risk of lung cancer. For help quitting, we offer smoking cessation utilizing the American Lung Association's Freedom From Smoking program. For more information about this program, call (561) 263-4351.


Radon is a radioactive gas made from the normal breakdown of uranium in soil and rocks. Uranium is found at higher levels in the soil in some parts of the United States. Radon can't be seen, tasted or smelled. It can build up indoors and create a possible risk for cancer. The lung cancer risk from radon is much lower than that from tobacco smoke, but is much higher in people who smoke than in those who don't. If you are concerned, contact State and local offices of the EPA (Environmental Protection Agency) for information on testing radon levels in your home.


Asbestos exposure is another risk factor for lung cancer. People who work with asbestos have a higher risk of getting lung cancer. If they also smoke, the risk is greatly increased. Both smokers and non-smokers exposed to asbestos also have a greater risk of developing a type of cancer that starts in the lining of the lungs, called mesothelioma.

Although asbestos was used for many years, the government has now nearly stopped its use in the workplace and in home products. While it is still present in many buildings, it is not thought to be harmful as long as it is not released into the air.

Other Cancer-Causing Agents in the Workplace

Other things that cause cancer can be found in some workplaces and can increase lung cancer risk include:

  • Radioactive ores, such as uranium
  • Inhaled chemicals or minerals like arsenic, beryllium, cadmium, silica, vinyl chloride, nickel compounds, chromium compounds, coal products, mustard gas, and chloromethyl ethers
  • Diesel exhaust

Major steps have been taken in recent years to help protect workers, but the dangers are still there. If you work around any of these, you should be very careful to limit your exposure as much as you can.

Radiation Treatment to the Lungs

People who have had radiation to the chest to treat other cancers are at higher risk for lung cancer, especially if they smoke. Women who have radiation to the breast after a lumpectomy for breast cancer do not appear to have a higher risk of lung cancer.


High levels of arsenic in drinking water may increase the risk of lung cancer. The effect is even greater for smokers.

Personal or Family History of Lung Cancer

If you have had lung cancer, you have a higher risk of getting another lung cancer. Brothers, sisters and children of people who have had lung cancer may have a slightly higher risk themselves, especially if the relative was diagnosed at a younger age.

Certain Vitamins

Two large studies have found that smokers who took beta carotene supplements actually had an increased risk of lung cancer. The results of these studies suggest that smokers should not take beta carotene supplements.

Air Pollution

In cities, air pollution may slightly increase the risk of lung cancer. But the risk is still far less than that caused by smoking. Worldwide, about five percent of all deaths from lung cancer may be due to outdoor air pollution.

DNA and Gene Changes

During the past few years, scientists have made great progress in learning how risk factors cause certain changes in the DNA (genetic material that carries the instructions for nearly everything our cells do) of lung cells, causing the cells to become cancerous.

Current research in this field is aimed at developing tests that can find lung cancers at an early stage by spotting DNA changes. But these tests are not yet ready for routine use.


To learn more, please call 561-263-4400 to schedule a consult.