Carcinogenic risk assessment: are there dose thresholds for carcinogens?

Area of Science:

• Toxicology
• Carcinogenesis
• Molecular Biology

Background:

• Genotoxic carcinogens are widely believed to lack a safe dose threshold.
• Emerging evidence suggests low doses may not induce tumors or preneoplastic lesions.

Purpose of the Study:

• To investigate the existence of a practical dose threshold for genotoxic carcinogens.
• To explore the potential for physiological adaptation to low-dose DNA-damaging agents.

Main Methods:

• Review of existing literature on genotoxic and non-genotoxic carcinogens.
• Analysis of dose-response relationships for various carcinogenic compounds.
• Examination of histopathological data at different exposure levels.

Main Results:

• Both genotoxic (e.g., heterocyclic amines, nitrosamines) and non-genotoxic (e.g., phenobarbital) agents may exhibit a practical dose threshold.
• Low doses of DNA-damaging agents might not cause assessable lesions.
• Hormesis or paradoxical protection may occur with non-genotoxic agents at very low doses.

Conclusions:

• The concept of a strict no-threshold for genotoxic carcinogens may require re-evaluation.
• Physiological adaptation is a plausible mechanism for mitigating low-dose genotoxic effects.
• Further research into low-dose effects and hormesis is warranted.