National and international agencies have established systems to classify agents according to the likelihood that the agent may cause cancer. This is often a difficult process because the information on an agent may be incomplete or inconclusive. Data from any human epidemiology studies are evaluated first, followed by information from animal studies. The International Agency for Research on Cancer (IARC) has developed one of the most comprehensive classification schemes. In this scheme an agent is rated from 1 to 4 based on human and animal data (see table below). Other classification schemes are in use by the U.S. EPA, National Toxicology Program, National Institute of Occupational Health Sciences (NIOSH), and the State of California.

IARC Classification Scheme for Carcinogenicity of Chemical and Physical Agents

 (Source: IARC - Preamble to the IARC Monographs, 2006)

Government regulatory agencies do not always agree on the classification of cancer-causing compounds and there are several different schemes, used by different agencies. Elaborate animal study protocols are used to determine if an agent may cause cancer.

Next: Recommendations and Conclusions

Back to cancer main page