Epidemiologic Study of Cancer

Because of the variation in the incidence of diffraent forms of cancer, it became recognized that environmental, occupational, and lifestyle factors play a major role in cancer risk. As early as 1964, the WHO declared that 75% of all human cancer was affected by extrinsic factors. In 1965, Ihe Intranational Agency for Research on Cancer (lARC) was created to focus on human cancer and Ihe relationship of humans to their environment. 

This chapter discusses (1) important issues relating to the study of cancer, 

The most commonly used demographic variables in epidemiology are age, race, and gender. Because these variables are relatively easy to study, a considerable amount of data has been amassed on these factors as they relate to cancer risk. 

Cancer has often been called a disease of old age. For most cancers, the incidence does increase with age, but that is not the case for all cancers. For example, the median age at diagnosis of testicular cancer is 34, and incidence 

TABLE 15.1. Incidence Rate per 100,000 of Selected Cancers by Age, Race/Ethnicity, and Sex-United States, 2001-2005 (SEER, 2008) 

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J. C. Contassot and co-workers, "Epidemiological Study of Cancer Morbidity Among Workers Exposed to Hydrazine," poster presented at the XXII International Congress on Occupational Health, in Sydney, AustraUa, Sept.—Oct., 1987. 

Li SQ, Dong QN, Liu YQ, et al Epidemiologic study of cancer mortality among chloroprene workers. Biomed Environ Sci 2 141-149, 1989... 

Three types of epidemiological studies of cancer contribute to the assessment of carcinogenicity in humans—cohort studies, case-control studies and correlation (or ecological) studies. Rarely, results from randomized trials may be available. Case series and case reports of cancer in humans may also be reviewed. 

The adequacy of epidemiological studies of reproductive outcome and genetic and related effects in humans is evaluated by the same criteria as are applied to epidemiological studies of cancer. 

Overinterpretation of laboratory and epidemiologic studies of cancer causation can make cancer-prevention regulations inefficient and ineffective. Similarly, it can lead to unjust resolution of cancer-related toxic torts. In this book VanDoren explains how these difficulties arise and gives valuable insight into how they can be reduced or eliminated by market-driven choices of individuals and companies. ... 

Hagmar L, Welinder H, Linden K, AtteweU R, Osterman-Golkar S, Tornqvist M. An epidemiological study of cancer risk among workers exposed to ethylene oxide using hemoglobin adducts to validate environmental exposure assessments. Int Arch Occup Environ Health 1991 63(4) 271-7. 

There are no data to verify if the above chronic effects seen in animals are also seen in humans. No epidemiological studies of cancer have been conducted. 

Meta-analysis of Epidemiology Studies of Cancer of the Nose and Nasal Sinuses and Nasopharyngeal Cancer... 

Redmond CK. 1976. Epidemiological studies of cancer mortality in coke plant workers Proceedings of the annual conference on environmental toxicology. Aerospace Medical Research Lab, Wright-Patterson AFB, OH. AMRL-TR-76-125. 

Considering its relatively long history of widespread use, it is remarkable that epidemiological studies of cancer risk focused on DDT exposure are almost non-existent. Ditraglia et al (61) studied mortality in workers from four organochlorine pesticide manufacturing plants, one of which had solely manufactured DDT since 1947. Cohorts were defined as all workers who had been employed for at least six months prior to 1965 and vital status was ascertained up to 1976. For the DDT plant a total of 6 cancer deaths were found leading to the calculation of an SMR of... 

The wear products of MOM joint articulahon are transported systemically and are manifested in elevated chromium and cobalt levels in a patient s serum and urine, raising the potential risk for carcinogenesis (Jacobs et al. 1996, Jacobs et al. 1998, Jacobs et al. 1999). However, epidemiological studies of cancer risk in patients with MOM remain inconclusive, because of the relatively small... 

Bjetke, E. Epidemiologic studies of cancer of the stomach, colon, and rectum, with special emphasis on the role of diet. Scand. J. Gastroenterol.. 9 (Suppl. 31) 1-235.1974. 

The wear products of MOM joint articulation are transported systemically and are manifested in elevated chromium and cobalt levels in a patient s serum and urine, raising the pKJtential risk for carcinogenesis [36, 69, 70]. However, epidemiological studies of cancer risk in patients with MOM remain inconclusive, due to the relatively small patient populations evaluated, the Scandinavian basis of the studies, and the typically rare incidence of the disease [35, 72]. There have also been reports of metal hypersensitivity associated with the implantation of MOM pros-theses, but the incidence of this complication is reported to be extremely rare [73]. Hypersensitivity may manifest itself in the form of an allergic response on the patient s skin however, there is no accepted clinical test to reliably test a patent s sensitivity to metals [74]. It remains unclear whether metal hypersensitivity is a contributing factor to implant performance or survivorship. 

As is evident from this example, the process starts with identifying general trends, getting more and more specific as you try to eliminate other sources or causes from consideration. The process usually doesn t work as clearly as shown above. As the U.S. ERA reports, it is unprecedented for such consistent results to be seen in epidemiological studies of cancer from environmental levels of a chemical or chemical mixture. In other words, it is rare that epidemiology alone can be used to link cause and effect. This is due to the many variables that are typically not consistent across all the people included in the studies. These variables that influence toxicity are discussed in chapter 6. 

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