New aspects in the classification of carcinogens

Area of Science:

• Toxicology
• Carcinogenesis
• Risk Assessment

Background:

• Current carcinogen classification systems lack a clear distinction between genotoxic and non-genotoxic agents.
• Non-genotoxic chemicals may have established permissible exposure levels with no anticipated human cancer risk.
• Genotoxic carcinogens can cause chromosomal damage through mutagenic or non-mutagenic pathways.

Purpose of the Study:

• To emphasize the need for differentiating genotoxic and non-genotoxic chemicals in carcinogen classification.
• To explore the dose-response relationships and threshold concepts for different types of carcinogens.
• To evaluate the impact of reactive oxygen species (ROS) and endogenous carcinogens on risk assessment.

Main Methods:

• Review of existing classification systems for carcinogens.
• Analysis of mechanisms of genotoxicity, including clastogenicity and aneugenicity.
• Consideration of dose-effect relationships for non-DNA-reactive genotoxins and ROS-inducing agents.

Main Results:

• Non-genotoxic chemicals allow for the derivation of safe exposure levels.
• Certain genotoxins, like those affecting topoisomerase or spindle apparatus, are carcinogenic only at high, toxic doses.
• Carcinogenesis mechanisms involving reactive oxygen species (ROS) may exhibit practical thresholds.

Conclusions:

• A clear distinction between genotoxic and non-genotoxic carcinogens is crucial for accurate risk assessment.
• Understanding the mode of action is essential for extrapolating carcinogenic risk to low doses, particularly considering endogenous carcinogens and ROS.
• Non-linear dose-effect relationships may occur for genotoxic chemicals, especially those involving ROS.