Carcinogenicity of smokeless tobacco: Evidence from studies in humans & experimental animals

A Working Group of the Monographs programme of the International Agency for Research on Cancer has classified smokeless tobacco as carcinogenic to humans (Group 1). This review article summarizes the data that support the evaluations of sufficient evidence in humans and in experimental animals for the carcinogenicity of smokeless tobacco whether used alone or with betel quid. It also identifies compounds of smokeless tobacco relevant to carcinogenicity (prominently tobacco-specific nitrosamines) and addiction (nicotine). The epidemiological evidence is summarized for oral cancer, other cancers associated with smokeless tobacco and oral potentially malignant lesions with a focus on analytical studies from the SEARO Region. Studies on cancer in experimental animals are summarized with a focus on studies applying smokeless tobacco products typical for the regions, such as mishri and naswar.