TLV carcinogenicity categories: Recent modifications

In 1992, the American Conference of Governmental Industrial Hygienists (ACGIH®) Chemical Substances Threshold Limit Values (TLVs®) Committee adopted a five-category system for classifying the carcinogenicity of industrial chemicals, processes, and agents. At that time, the decision of the TLV Committee was to adopt a system which agreed as closely as possible with the system developed by the International Agency for Research on Cancer (IARC). Recent scientific and international developments, such as attempts at harmonization of occupational exposure guidelines, as well as the passage of time, have caused the TLV Committee to revisit the issue of how best to classify carcinogenicity. The objective of this article is to describe recent changes in classifying carcinogenicity by the TLV Committee and to examine these changes in relationship to the classification systems used by other groups, particularly the German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (the MAK Commission). A description is provided of how decisions on carcinogenicity classification are made by the TLV Committee and how the decision process may differ from that of other groups. The changes made since 1992 have been evolutionary in nature, following meetings with the MAK Commission and internal discussions within the committee. Information on mechanism of action will play a greater role in classifying carcinogenicity.