Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options

What You Need to Know. What You Can Do.
How do scientists decide which substances to test in animals, human laboratory cells, or human population studies?

Learning Objective

Upon completion of this section, you will be able to

  • Explain how scientists decide which substances to test in animals, human laboratory cells, or human population studies.

Strategies for Testing in Animals or Human Laboratory Cells

Because resources are limited, scientists must decide out of thousands of candidates which substances to select for testing in animals or in human cells. The tests are costly and time-consuming: determining whether a chemical causes cancer in rats or mice can cost several million dollars and take several years to complete. Three factors generally guide the decision to test a substance.

The Number of People Exposed

We want to test those chemicals that affect a large number of people or those for which the exposure levels have been unusually high. Pesticides, for example, fit both categories. They potentially affect a large number of people because of trace amounts on foods and their use in or around the home, and in farming-related occupations, exposure levels are high.

Previous Data

This could be a report that in laboratory cells, a chemical causes alterations in human DNA. Or it could be a report that people exposed to a particular chemical in the workplace or at a specific geographical location have developed specific cancers at higher rates than expected. This kind of information provides important clues for decisions about animal testing. Even before any animal testing was done, studies on human and animal cells indicated dioxins and polycyclic aromatic hydrocarbons were suspected carcinogens.

Public Concern

Chromium and some pesticides are examples of a group of concerned citizens first bringing to the attention of public health officials concerns about chemicals. The National Toxicology Program has a Web site available to the public to suggest agents suspected of causing cancer: ntp-server.niehs.nih.gov; click on “ Nominations to the Testing Program.”

Strategies for Carrying out Large Population Studies

Similar considerations guide epidemiologists as to whether to begin large population studies. Some of these factors include

  • Animal study data suggesting a cancer-exposure link (e.g., vinyl chloride) or a related agent that raises suspicion (e.g., acrylonitrile was studied because of its structural similarity to vinyl chloride).
  • Results from other epidemiologic studies (large population studies) that suggest the need for additional studies
  • An exposure’s biological mechanisms that suggest a possible link to cancer.
  • Pockets of specific cancers that cluster in a particular town or place or unusual case reports.
  • Cancer trends—that is, rates that change over time or with location.
  • Changes in cancer rates within a population after migration to a new area.
  • Introduction of a new exposure or technology for which epidemiologic data are needed, or an unusual exposure pattern needing evaluation.

Key Points

  • Resources are limited. Scientists must decide out of thousands of candidates which substances should be selected for animals or human cell testing. Tests are costly and time-consuming.
    • Accordingly, we want to test
      • Those chemicals that affect a large number of people, or
      • Those for which the exposure levels have been unusually high, or
      • We might want to test both.
    • Previous data provide important clues for decisions about animal testing. For example
      • A chemical causes alterations in human DNA in laboratory cells, or
      • A report that people exposed to a particular chemical in the workplace, or
      • A report that people at a specific geographical location are getting cancer at higher rates than expected, or
      • A combination of all three.
    • On occasion, a group of citizens first bring their concerns about chemicals to the attention of public health officials.
  • Similar considerations guide epidemiologists as to whether to begin large population studies.
Progress Check

Choose the best answer.

1. In deciding which substances should be selected for testing in animals or with human cells, scientists DO NOT use?

A. Chemicals that affect a large number of persons or chemicals for which exposure levels have been unusually high.
B. Chemicals that in laboratory cells cause human DNA alterations.
C. Reports that people exposed to a particular chemical in the workplace develop certain cancers at rates similar to the general population.
D. Chemicals that concerned citizens groups first brought to the attention of public health officials.

Answer:

To review relevant content, see Strategies for Testing in Animals or Human Laboratory Cells in this section.

2. Which of the following factors ARE NOT TAKEN INTO CONSIDERATION by epidemiologists when beginning large population studies?

A. Data from animal studies suggesting a cancer-exposure link.
B. Cancer trends or rates that do not change over time or with location.
C. Changes in cancer rates within a population after that population has migrated to new area.
D. Pockets of cancers that cluster in a particular town or place or that are the subjects of unusual case reports.

Answer:

To review relevant content, see Strategies for Carrying out Large Population Studies in this section.


Previous Section Next Section
 
Contact Us:
  • Agency for Toxic Substances and Disease Registry
    4770 Buford Hwy NE
    Atlanta, GA 30341
  • 800-CDC-INFO
    (800-232-4636)
    TTY: (888) 232-6348
    Contact CDC-INFO
  • New Hours of Operation
    8am-8pm ET/Monday-Friday
    Closed Holidays
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #