Arsenic and cancer: the still unanswered question.

For some 2,500 years, arsenic was considered an important element of pharmacopeias and was praised for its medicinal qualities. However, an incidental link with cancer was suggested during the nineteenth century, and since that time a controversy has ensued with regard to the compound's tumorigenicity. Several epidemiological surveys, for example, have suggested that arsenic induces lung, liver, or skin cancer in humans. On the other hand, all experimental attempts to reproduce such neoplasms in laboratory animals have consistently failed, thereby denying support to the human data. Recently arsenic was reported to be mutagenic. However, because of the inconsistency of most mutagenesis findings at present, this also cannot be regarded as supporting evidence. Furthermore, a recent trend has been to consider arsenic as beneficial in cancer prevention and in maintaining the health of farm animals, and, perhaps, humans. A critical review of epidemiological and experimental data from the literature has been made in an attempt to present an objective picture of this controversial and sensitive question and to encourage further research, which may ultimately determine whether arsenic deserves its execrable reputation.