[The bystander effect: potential impact on risk assessment of carcinogen agents]

A growing experimental evidence indicates that ionizing radiation is able to determine relevant biological effects, included SCE and micronuclei induction, gene mutations, ROS production and gene expression modification, in cells not directly hit by radiation. Such a phenomenon, known as bystander effect, has been described for different types of radiation (alpha, gamma, X and beta) and cells and it is relevant at low doses (also few mGy). It is likely to be mediated by either diffusible factors released by irradiated cells or the passage of mediators through gap junctions; in many cases it seems to be persistent over time. Until now, the bystander effect has been primarily described in vitro for ionizing radiation. A crucial outcome of future research deals with the existence and quantification of this effect in relation to chemical agents displaying genotoxic and carcinogenic potential.