Figure 2.

Proposed carcinogenic roles for different chemical compounds underlining the relevance of ‘immortalization’ compounds. (I) Compound acting on somatic cells at different levels (DNA-damage for example) Compound A may induce senescence. (II) The same compound A acting on a stem cell that does not have replicative constraints will induce tumorigenesis. (III) If the same compound A acts after an ‘immortalization’ compound (compound B) that overrides the senescence barrier, the compound will be carcinogenic in these somatic cells. (IV) Similar to III, but in this case, both compounds act in a mixture.