Quantification of the role of smoking and chewing tobacco in oral, pharyngeal, and oesophageal cancers.

The aetiologic fractions due to smoking and chewing tobacco have been quantified for the first time, for cancers of the oral cavity, oropharynx, hypopharynx, larynx and oesophagus. The overall aetiologic fractions due to smoking and/or chewing tobacco have been found to be 70% for cancer of the oral cavity, 84% for the oropharynx, and about 75% for the hypopharynx and larynx. In cancer of the oesophagus, however, the fraction is only 50%, showing that another factor or factors play an equal role in the aetiology of cancer of this site. At each of the sites studied, it was found that the two factors, smoking and chewing, acted synergistically, though in varying degrees.