[Classification as carcinogenic for 2,3,7,8-tetrachlorodibenzo-para-dioxin: an eventful journey].

Carcinogenicity of 2,3,7,8-tetrachlorodibenzo-para-dioxin (2,3,7,8-TCDD) and some other dioxin congeners is long time discussed by epidemiological and experimental studies, often with conflicting findings. The inclusion of 2,3,7,8-TCDD in Group 1 by 1ARC in 1997 was based essentially on mechanistic evidence and experimental studies despite the limited evidence in humans. This procedure generated a lot of controversy. Some scientists agree with this classification and sometimes suggested increased cancer mortality risk with TCDD daily intake similar to those of the general population. Other authors re-analyzing data mainly from caselist previously investigated did not confirm the 2,3,7,8-TCDD carcinogenicity. In the review process of carcinogenic substances by IARC in 2010, the evidence for 2,3,7,8-TCDD carcinogenicity in humans upgraded from limited to sufficient, due to confirmed and integrated epidemiological evidences. It is also confirmed that these findings relate to all cancers combined, while for some "classic" cancers related to TCDD (as soft tissue sarcoma and non-Hodgkin lymphoma) the evidence remains limited. In this paper a literature review accompanied by comments is reported with the aim to provide information about the evaluation process and tools for its more critical and scrupulous interpretation.