Chemical-induced cancer

Immunodeficiency has been associated with an increased incidence of viral-induced cancers, which tend to be more immunogenic than those that are chemically-induced. Cancers related to immunosuppression include leukemia and cancers of the skin (seen in transplant patients4) as well as Kaposi s sarcoma and EB V-associated B cell lymphomas (observed in HIV/AIDS patients). 

Apart from differences in the age-distribution of chemically-induced cancers, to be discussed below, the limited data on such neoplasmas... 

Distribution of Chemically Induced Cancers in Relation to Time after Exposure... 

However, given the current state of knowledge and methods of dose-response assessment for substances that cause stochastic responses, there appear to be important technical and institutional impediments to the use of either incidence or fatalities exclusively. Data on radiation-induced cancer incidence and chemical-induced cancer fatalities for use at the low doses and dose rates relevant to health protection are not readily available, and current regulatory guidance calls for calculation of cancer incidence for hazardous chemicals. Since use of a common measure of response for all substances that cause stochastic responses may not be practical in the near term, both measures (fatalities for radionuclides and incidence for hazardous chemicals) could be used in the interest of expediency. The primary advantage of this approach is that the measures of stochastic response for radionuclides and hazardous chemicals would be based on the best available information from studies in humans and animals, and it would involve the fewest subjective modifying factors. This approach also would be the easiest to implement. 

Over the past ten years the role of various levels and types of dietary fat and dietary antioxidants in modifying chemically induced cancer has been actively investigated in this laboratory with most of the work centering on mammary cancer. 

Table I. Influence of Selenium on Chemically Induced Cancer...

There are no reported feeding studies showing protection by broccoli against chemically induced cancers in animal models. However, there is an abundant... 

Decrease in tumor incidence was one of the first observed favorable effects of reduced food intake observed in experiments conducted in early twentieth century. Since then substantial evidence has shown that DR results in inhibition of tumor promotion and decreases in both spontaneous and chemical-induced cancer incidence. 

Induction of Morphological and Neoplastic Transformation in Mammalian Cells Cell Culture Models for Chemically Induced Cancer Proceeding through Mutagenesis... 

In some experimental studies, L-tryptophan has been observed to have a protective or inhibitory effect against chemically induced cancers. A possible explanation appears to rely on the ability of tryptophan or its metabolite to enhance the activities of many enzymes, some of which are... 

Trauma appears to play an important role in cancer. Any long-lasting wound or sore is considered a potential site for cancer and is thus listed as one of the warning signs. It has been shown that wound healing alone can promote the formation of skin tumors initiated by DMBA (20). As pointed out later in this chapter, inflammation and cellular proliferation are related to chemically induced cancer. Chemical carcinogens and tumor promoters induce inflammation and hyperplasia in mouse skin, but it is also known that not all inflammatory-hyperplastic agents cause skin cancer or promote it (21). 

During the past twenty years, two major trends of relevance to this symposium have become evident. First, the number of identified rodent carcinogens has increased more than could have been anticipated, almost to the point that non-carcinogens have now become the rarity. Second, the projected epidemic of chemically-induced cancers in man has not come to pass. Given the apparent conflict between these two trends, a... 

During the latter half of the 20 century, epidemiology moved beyond epidemics and infectious diseases. Its techniques have been adapted to identifying a variety of sources of diseases, including chemically induced cancer. Presently, epidemiology is defined as the study of the distribution and determination of health-related states and events in specified populations and the application of this study to the control of health problems. 

Protection against a chemical-induced cancer by Chlorella vulgaris administration... 

Furthermore, because of the long latent period of 20-30 years between initial exposure and the appearance of chemically induced cancers, and the even greater period of time it may take before the accumulation of recessive germline mutations become evident, an epidemiologic approach is impractical for assessing carcinogenic or mutagenic hazards associated with a newly synthesized chemical. 

Strategy for Preventing Chemically-Induced Cancer in Humans... 

Cancer of the skin became the first experimental model of chemically induced cancer in 1915 when Yamagiwa and Ichikawa/ in Japan, induced skin carcinomas in the ears of rabbits by repeated topical applications of coal tar for long periods (see ). In 1918, Tsutsui induced skin cancer in mice with tars and/ in 1922, Passey induced skin cancer in mice with ether extracts of tars (5). 

Cancer of the liver, the first experimental visceral cancer, became a model of chemically induced cancer in 1933 when Yoshida induced liver tumors in rats and mice with oral administrations of o-aminoazotoluene (2, 3-dimethyl-4-aminoazobenzene) ( ). ... 

Correlations exist between manganese toxicity and exposure to other toxic substances in the environment, such as ozone [540-542] against which the element offers some protection against radical oxidative damage, or susceptibility to chemically induced cancer [543], cadmium [544,545], other trace elements [546], and alcohol [547]. Lysosomes in the brain have been found to play a role in manganese toxicity [548], and mechanisms for pulmonary clearance of soluble and insoluble forms of the element manganese have been discussed by Drown et al. [549]. 

It is these last two properties which underlie the seriousness of cancer as an adverse health effect. Chemically induced cancer may arise as a result of mutagenic properties possessed by a substance or metabolite causing a mutation in the target cells, which leads to expression as cancer when these cells divide. A substance causing cancer by this mechanism is known as a genotoxic carcinogen. 

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