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Because we in the study of carcinogenesis can get so involved in the multiple factorial nature, I would like to preface all the remarks which are to follow by a quote from Dr. Hueper 1 that I believe is appropriate in a discussion of OCCUpational cancer: ". , . there is no cancer without a carcinogen. . . ." t In this presentation I would like to comment first on the early recognition by investigators of the multiple factorial nature of carcinogenesis. Next, the component factors that relate to the host and the agent (or the actual exposure) will be treated. I will then present remarks concerning the significance of multiple factors in occupational cancer, and will close with comments on the broader ramifications of these significant points.Physicians of the early nineteenth century recognized that multiple factors influence the development of occupational cancer. With the exception of the chimney sweeps' cancer, which was reported in the eighteenth century,2 these were the first reports of occupational cancer. Early in the twentieth century, Alexander Scott, in 1923,3 described the skin lesions of the Scottish shale-oil workers. He revealed an appreciation of multiple factors when he said, "Accumulated evidence tends to show that some workmen have a greater tendency to be affected than others, the working conditions otherwise being the same."

Dibenzo‐ p ‐dioxins are a class of compounds of which there are 75 possible isomers as shown. A recent IARC Monograph summarizes much of the information on these compounds. By far, the majority of the information is for 2,3,7,8‐tetrachlorodibenzo‐ p ‐dioxin (TCDD), the most toxic of the isomers. Most of the material in this chapter relates to this compound.