Module 3: Toxicology - Section 13: Occupational Carcinogenesis

TOX 13.7: Epidemiological Issues in Occupational Cancers

EPIDEMIOLOGICAL ISSUES IN OCCUPATIONAL CANCERS:

In order to definitively determine the cause effect relationship between exposures and cancers in the workplace, sound epidemiological data is necessary. However there exists several problems in trying to determine such effects. An important factors in this is the confounding by other non-occupational exposures and the lack of information to determine the role of confounders. Co-carcinogenic factors are also important. These could be occupational and non-occupational eg. diet, tobacco and alcohol. (Eg. The role of smoking in asbestos exposure and the multiplicative effect in lung cancer). Long induction-latency periods ranging from 13 to 40 years is problematic and introduces a variety of biases in studies. Retrospective studies using death certificate data suffer from problems related to misclassification and lack of occupational information.

The issue of dose response and threshold levels with carcinogens remains an area of theoretical debate. With the multistage theory of carcinogenesis, implying the involvement of several factors, attempting to determine a "safe" dose of exposure is problematic, and is generally not accepted.

CLINICAL APPLICATION OF CLASSIFICATION:

In attempting to determine causation in an individual, a variety of factors need to be considered, including epidemiological considerations, specificity of exposure/cancer relationship, statistical probability and IARC review of the agent. The following need to be answered:

• To what agent, mixture or exposure circumstance was the patient exposed?
• Does this cause the specific type of cancer at any exposure level?
• Was this patient’s exposure heavy enough (intensity and duration) to have increased his risk with a high degree of certainty?
• Did sufficient time elapse between onset of exposure and cancer?
• Are there any alternative causative explanations ?

OCCUPATIONS INVOLVING A CARCINOGENIC RISK:

Lack of adequate information about work processes results in an inability to define at risk occupations. Furthermore the rapid progress within industry and work processes result in the changing of workplace exposures. The following table lists some  occupations and exposures which place workers at risk for cancer. The table is based on the IARC classification group 1.  The full list of all current accepted and suspected causes by IARC can also be consulted.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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