David learns
                                                             what cancer is 
                                                             and how it 


Why do people get cancer?


Ninety percent of cancers develop because of complex interactions between our bodies, our lifestyles, our genetic makeup and our environment. Scientists have discovered different factors that cause cancer. Research shows that tobacco is estimated to cause 30 percent of all cancer deaths, poor diet 35 percent, reproductive and sexual behavior seven percent, work-related causes four percent and the environment itself causes three percent.

Scientists believe that genetic changes, whether inherited or acquired, are the basic cause of cancer. Some scientific theories do suggest that cancer may be a hereditary disease because each individual's make-up may make them more susceptible to certain cancers. About 50 of the more than 120 different types of cancer occasionally run in families.

Most of the current scientific evidence indicates that a normal cell can become transformed into a cancer cell when certain genes become activated. Recent work in cancer biology concerns the study of oncogenes, a specific gene that participates in changing a normal cell into a cancer cell. It is thought that an oncogene might be present in an inactive form in normal cells and is some way activated to create cancer cells.

As mentioned, the nature of a person's work or the working environment can also be a factor in developing cancer. The chart below identifies several cancer-causing agents, occupations where this exposure occurs and the types of cancers that can develop.

Ultraviolet Farmers, Sailors, Skin Light Lifeguards, Everyone
Radon Underground Miners Lung (example- uranium)
Asbestos Asbestos workers, Lung Insulation workers
Benzene Workers who use glue, Marrow varnishes, etc. (Leukemia)
X-rays, Radium Radiologists Skin

Things to Talk About

  1. Can you develop cancer at any age?
  2. Are some cancers more deadly than others?
  3. What substances are carcinogens? What different types of cancer may they cause?

Carcinogen--A substance or agent that encourages the growth of cancer cells.

Carcinoma--A cancer which is a malignant growth of epithelial tissue or the tissue that forms the skin or blood vessels in an organism (e.g., the surface cells of the skin and the inside of the blood vessels).

Sarcoma--A cancer which is the malignant growth of connective tissue.

Leukemia--Cancer of the blood-forming tissues.


Additional Sources of Information

Activity Page

Take a Close-Up!

Learn about human cells by taking a close look at your own.

Main Activity

You will take a small sample of the epithelial cells that line the inside of your mouth. You'll get a glimpse of how scientists investigate inside cells.


1. Place a drop of stain on a microscope slide.

2. Gently scrape the inside of your cheek with the flat edge of a toothpick.

3. Dip this edge of the toothpick in the drop of stain on the slide.

4. Take another toothpick and once again scrape the inside of your cheek with the flat edge, and dip the second toothpick into the stain.

5. Spread the stain and cheek cells around in a small area with the toothpick and cover the slide with a cover slip.

6. First look at the slide under the low-power lens of the microscope. Focus carefully and record your observations. Now observe the slide under the high-power lens.


1. How do the cells appear under low-power and high-power lenses? Outline the characteristics and highlight the similarities and differences.

2. Why was the iodine stain necessary for this activity?

3. Compare your cheek cells with your classmates. Are everyone's cells the same?

4. How long can cells live? What are examples of different types of cells and their life spans?

5. If cells live for different lengths of time, how are new cells added? Are all cells that die replaced?

Countries frequently have very different rates of cancer incidence. Try to determine which countries have high rates of rare cancers or high rates of one specific kind of cancer. Develop a data table which includes the country, type of cancer and cause.

Find out how the invention of the microscope helped scientists better understand the structure of the cell and how that structure is altered by carcinogens. How is an electron microscope different from the kind of microscopes you have in your science laboratory?

Do some research on different environmental and lifestyle factors that cause cancer. Find out how pollution, tobacco and eating habits can increase the risk of cancer. Make a list of things you can do that might prevent cancer.

Find out how scientists, biologists and chemists determine if materials are carcinogens. Why are scientists concerned about asbestos and radon? Find out if your school has been inspected for asbestos. What kinds of precautions do people take when it is removed?

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Newton's Apple is a production of KTCA Twin Cities Public Television. Made possible by a grant from 3M.

Educational materials developed with the National Science Teachers Association.

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