Cancer Clusters

A woman s lifetime risk of breast cancer is approximately 1 in 8, Breast cancer clusters in families the risk of breast cancer doubles for a woman with one affected first-degree relative (e.g., mother, sister, or daughter). The risk increases further if there are multiple affected relatives or if the relatives developed early-onset breast cancer. 

Case reports of testicular cancer in aircraft repair and leather tannery facilities suggested possible association with dimethylformamide. Further research has failed to confirm this relationship. A screening effort at a leather tannery, where a cancer cluster had been noted, identified no additional cases. Mortality and cancer incidence studies and nested case-control investigations of testicular cancer and several other anatomical sites at several facilities with exposure to dimethylformamide noted no convincing associations. 

Zeliger HI. Unexplained cancer clusters common threads. Arch Environ Health 2004 59(4) 172-6. 

The complexities of the mixtures just described make it difficult to ascribe the increased lung cancer rates to any particular chemical or mixture. All the above exposures are to mixtures of lipophiles and hydrophiles, which have been shown to be associated with unexplained cancer clusters J94l... 

Wilkins JR III, McLaughlin JA, Sinks TH, et al. Parental occupation and intracranial neoplasms of childhood Anecdotal evidence from a unique occupational cancer cluster. J Am IndMed 1991 19 643 53. 

It is most probable that the causative agent for prostate cancer in leather tannery workers is a mixture of unknown composition. Working in the leather tanning industry is more commonly associated with increased prevalence of testicular cancer clusters. 7375 This is discussed in Chapter 34. 

Ducatman A, Crawl JR, Conwill DE. Cancer clusters Correlation, causation, and common sense. Chemtech 1988 4 204-10. 

Many studies have been carried out on the effects of environmental chemical exposure and carcinogenesis in children, beginning in utero and through their teens. The following are representative of these studies where chemical mixtures were shown to be causative. Other examples are examined in the next chapter on cancer clusters. 

Children are at greater risk than adults for many cancers. Leukemia and brain cancer account for half of all childhood cancers. The causes of these cancers are often obscure, but research has shown that in utero exposures can start the carcinogenic process that becomes fully manifest after birth. Mixtures of chemicals, most notably tobacco smoke and pesticides, are known causative childhood cancer agents. Other chemical mixtures identified as carcinogenic to children are examined in the next chapter on cancer clusters. 

Many cancer clusters have been associated with exposures to individual chemicals. A number of these, however, have followed exposures to mixtures of chemicals. Those who have investigated these mixture exposure clusters have focused their attention on finding the individual components of the mixtures that were the causative agents. 

It is hypothesized here that the mixtures, and not single components of these mixtures, are the causative agents for many cancer clusters. Several previously unexplained cancer clusters all have common elements ... 

The cancer clusters may be in the form of single cancers per cluster or of specific multiple cancers per cluster. 

The following are examples of cancer clusters reported in the literature that are unexpected, that is, that cannot be attributed to any single causative agent. In all cases, the cancer clusters followed exposures to mixtures of lipophiles and hydrophiles. Kow values are given for each chemical to demonstrate lipophilic or hydrophilic character. 

Three different testicular cancer clusters have been reported among leather tannery workersJ6-8 These workers are exposed to a wide range of lipophilic and hydrophilic chemicals that include... 

A testicular cancer cluster was also reported among military aircraft repair personnel The chemicals these workers were exposed to included... 

Cluster 7 Brain Cancer Cluster—Electronics Workers... 

A brain cancer cluster was found at an electronics components manufacturing plant. I10l The chemicals used in the plant included... 

Cluster 8 Brain Cancer Cluster—Petrochemical Workers... 

A brain cancer cluster was documented among petrochemical workers 11 The raw materials and chemicals manufactured in the plant included a broad range of lipophilic and hydrophilic compounds, among them... 

A unique cancer cluster was reported in which children of parents (both mothers or fathers) who worked at the same electronics manufacturing plant developed intracranial neoplasms.I12 Parents were exposed to some 30 different chemical classes containing more than 100 different compounds. These compounds included... 

The three cancer clusters just discussed are interesting to analyze. Two different sets of chemical mixtures (in electronics workers and petrochemical workers) induced brain cancers in those exposed, whereas in one instance (the second electronics worker group) only the children of those exposed developed brain cancer. These studies show that different mixtures of chemicals can induce the same cancer types and that different mechanisms are at work in the development of the same cancer type. In all three clusters, none of the individual chemicals that the workers were exposed to is known to be causative for brain cancer. 

A colorectal cancer cluster was reported in a polypropylene manufacturing plantJ15 The chemicals used included... 

A lung cancer cluster was identified in steel mill workers who worked in the melt shop of an electric steel-making operationJ18 That mill cast carbon and specialty steels from scrap metals. The raw materials for the plant included automobile industry scrap, construction materials, and containers that were coated with oil-based and other organic materials. Flue dust analysis revealed the following hydrophilic compounds ... 

Naval divers in Israel train in the Kishon River. Pollution in the Kishon River ranks among the highest in the world, reaching levels close to those in the Rhine, Alba, and Po rivers. Divers who have trained in these waters form a cancer cluster of multiple cancers that are not only far in excess of cancers in the general population, but also have very short induction periods. I24 The cancers found in the divers include... 

Most cancer cluster studies have focused on identifying single compound causative agents. Most of these clusters, however, result from exposures to mixtures of chemicals. Analysis of the cancer clusters reported in the literature, many of which are described above, reveals that all of the unexplained clusters ensue following exposures to chemical mixtures that contain at least one lipophilic and one hydrophilic chemical. These mixtures act as unique entities to produce specific cancer clusters whose locations are not predicted by the known toxicology of the single compounds that comprise the mixtures. 

Enterline PE. Evaluating cancer clusters. Am Ind Hyg Assoc J1985 43(6) BIO-13. 

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