For over 80 years doctors have known that too much alcohol can cause cancer but once again this well- established fact has been questioned because it proved impossible to induce the disease in laboratory animals. Indeed, some researchers insist that alcohol should not be classified as a human carcinogen because there is no evidence from animal experiments!34 The same is true for benzene, an industrial chemical widely used in manufacturing processes. According to the August 1982 issue of the scientific journal American Statistician,
“Although there are reliable human data linking benzene to leukemia, scientists have been reluctant to categorize benzene as a carcinogen because there are no published reports that it induces leukemia in rodents.”
Arsenic is yet another well known human carcinogen for which animal tests have proved persistently negative. Human population studies have identified cancers in people following exposure to arsenic in drinking water and medications, as well as in chemical and agricultural workers, and also in those mining the ore.35 By 1947 an historical review of the subject described how dozens of animal tests had given “only doubtful results,” but that some human cases seemed definitely linked to the chemical.36 In 1969 researchers at the National Cancer Institute stated37 that “arsenic has been suspected by many investigators as a carcinogen in man, though there is no supporting evidence from animal experiments.” And in 1977 a further scientific review still concluded35 that there is little evidence that arsenic compounds are carcinogenic in animals.” Finally, in 1987, scientists managed to produce cancer in animals. This was 180 years after arsenic was first suggested as a human carcinogen and over 70 years since the first attempt to induce the disease in animals.
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