As long ago as 1775, Percival Pot, a London surgeon, described the link between cancer of the scrotum and chimney sweeps' boys (Walter, 1977). Pot observed that there was a higher incidence of carcinoma of the scrotum in boys who worked sweeping chimneys than those employed in other occupations. Although not designed as a scientific study to establish the cause of cancer in this group of boys, a causal link was identified. Horton-Taylor (2001) writes about the study undertaken by Doll and Hill, in the 1950s, looking at the incidence of lung cancer among British doctors. This study established a link between smoking and the development of small cell (oat cell) carcinoma of the lung. Further work undertaken by Doll and Hill has identified that the risk of dying from lung cancer is 32 times higher in heavy smokers compared with non-smokers (Horton-Taylor, 2001). A laboratory experiment, undertaken in 1915, proved for the first time that it was possible to develop cancer as a direct result of exposure to a chemical - coal tar. It was applied directly to the skin of a rabbit, resulting in the development of skin cancer (Yarbro, 2000a). In 1896 a German physicist, Roentgen, identified the use of radiation (X-rays) as a diagnostic tool. Further work looking at the use of radiation resulted in it being used as a new treatment for cancer by the close of the nineteenth century. However, within 7 years of Roentgen discovering the use of X-rays as a diagnostic tool, a causal link between exposure to radiation and the development of leukaemia was established (Yarbro, 2000a).
At the beginning of the twenty-first century we have come a long way since Pot's chance observation identifying the cause of cancer of the scrotum in chimney sweeps' boys - the earliest described occu-pationally acquired malignancy. Studies are now undertaken specifically to identify whether there are causal links between exposure to certain substances and the development of cancer.
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