Epigenetic carcinogens: problems with identification and risk estimation.

The mechanisms of carcinogenesis are just beginning to be understood. There is recent interest in the broad classification of carcinogens into two categories based upon their mechanism of action: those that interact with DNA via a genetic mechanism are termed genetic carcinogens; and those that do not directly interact with DNA, but may cause changes in DNA tertiary structure or methylation patterns, and are termed epigenetic carcinogens. Present knowledge is inadequate to justify separate risk assessment methods for genetic vs. epigenetic carcinogens. Quantitative estimates of carcinogenic risk are currently best made using non-threshold models.