Course:SPPH381B/Essay 2/Occupational Cancer - Desiree

Occupational Cancer

History

The prevalence of cancer has increased in recent decades due to rapidly aging populations, the increasing risk of risky behaviour in the general population, and the increased presence of carcinogens in the environment . The oldest forms of mammalian tumors have been found in fossilized dinosaur and prehistoric human bones, and the first cancerous growths found in humans date back to approximately 1500 B.C., in Egyptian and Peruvian mummies . The first documented mention of cancer was written by Imhotep, approximately 4,600 years ago. This document, as well as others from that period of time, describe surgical, pharmacological, and magical treatments . There is mention of cancer throughout the ages and around World War II there are reports of an anticancer drug working efficiently, this agent was mustard gas, that had been used for chemical warfare in the First World War .

Types and means of proliferation

There are many different types of cancer. Carcinomas are cancer of the epithelial cells, sarcoma, of the soft tissue, leukemia, of the blood, lymphoma, of the lymphocytes, and melanoma, of the skin. A tumor develops when the transcription of DNA is disrupted which causes a mutation in the expression of the proteins and therefore in the function of the cells. These epigenetic mutations are responsible for the conversion of normal cells to tumor cells, either by mutations in genes which suppress cell growth (tumor suppressor genes) or genes that promote cell growth (proto-oncogenes) . A tumor occurs when the mutated cells proliferate without stopping. If cancerous cells from that tumor move from the initial location and become embedded in other tissues, the tumor is said to be a metastatic cancer. Cancers have long latency periods, it can take 10 to 60 years before the cancer and its symptoms are apparent.

Carcinogens

Although there are many determinants of cancer, such as genetics, physical activity, diet, smoking, and sun exposure, environmental factors, such as carcinogens, chemicals that cause cancer, are estimated to be associated with 60-90% of cancers . Common environmental cancer risks include exposure to asbestos, outdoor air pollution, tobacco smoke, radon exposure, inorganic arsenic in drinking water, and water chlorinated by-products . Some of these carcinogens are naturally occurring and are present in food and as produce of intestinal flora which have contact with human tissues at low doses .

Cancer in the workplace

Individuals are all susceptible to the risks associated with cancer, however, those in the workplace are additionally susceptible to the multitude of chemicals present in the workplace. These individuals, who have particular and unique exposures to chemicals, have a higher incidence of specific cancers . These exposures include asbestos, heavy metals, silica and mineral dusts, polycyclic aromatic hydrocarbons(like benzene), many reactive chemicals, and ionizing radiation . The best preventive measure of these cancers is the control of occupational exposures . According to the World Health Organization, cancers of the lung, trachea, and bronchus are the most common occupational cancers. For example, one in three deaths from occupational cancers is due to asbestos. These types of cancer make up 10.3% of cancer worldwide.

Risk Assessment

IARC (International Agency for Research on Cancer, part of WHO) classifies chemicals in different groups depending on their risk to humans. Chemicals in group 1 are classified as being carcinogenic to humans. Group 2A is probably carcinogenic to humans and chemicals in group 2B are possibly carcinogenic to humans. Chemicals may be classified as either 2A or 2B depending on whether or not there is human data available, a chemical may be assigned to a different classification if there is animal but not human data available for the carcinogenicity of the substance. Chemicals that are unclassifiable are in group 3 and group 4 includes chemicals that are probably not carcinogenic to humans. The purpose of this classification system is to " achieve a balanced evaluation of data. . . and to put into perspective the present state of knowledge with the final aim of evaluating the data in terms of possible human risk" . A list of agents, the group classification as well as the year they were classified can be found on the International Agency for Cancer Research website. The CAS number of each agent is also given and information pertaining to chemical and physical data, use and occurrence, biological data, and comments on data report and evaluation can be found on the website.

IARC classification (http://monographs.iarc.fr/ENG/Classification/)

Group	Effect	Number of agents	Examples
1	Carcinogenic to humans	119	Formaldehyde, Silica dust, Wood dust, Mustard gas
2A	Probably carcinogenic to humans	81	DDT (4,4'-Dichlorodiphenyltrichloroethane), Androgenic (anabolic) steroids
2B	Possibly carcinogenic to humans	292	Acetamide, Chloroform, Nickel, metallic and alloys
3	Not classifiable as to its carcinogenicity to humans	505	Caffeine, Cholesterol, Isopropyl alcohol, Polystyrene
4	Probably not carcinogenic to humans	1	Caprolactam

Cancer clusters

Cancer clusters are defined as greater than expected cancer cases in a restricted specific geographic area, time period, or group of people and they have been attributed to factors such as occupation, a particular medicine, or behaviours such as smoking or sunbathing . More than 1000 suspected cancer clusters are reported each year to state and local health departments, however, there are normally plausible explanations for the clustering, as a result few of them are true clusters . The reason there are so many reported cases is because in community settings cases may involve a mix of unrelated cancers and it is difficult to ascertain one cause as any exposure is low and poorly defined, in contrast, clusters in work places are easier to distinguish as the nature of the work involves high, prolonged, and well-defined exposure .

ALARA principle

ALARA stands for “As Low As Reasonably Achievable” and is implicated in setting exposure standards for exposure to carcinogenic substances . This principle however is quite vague as there is no standard definition for the terms “reasonably” and “achievable”, which leads to variation in the application of this principle.

Conclusion

Knowing or suspecting that a chemical causes a risk to the individuals handling it is not necessarily enough remove it from the manufacturing process. The benefit to society of using a certain agent in a product may be too great when compared to the possible risk to the individual, in such cases wide-spread prohibition becomes undesirable . In many cases a chemical is removed only to be replaced by an agent that is just as, or more dangerous than the previously used agent. This knowledge has incited the use of many regulations such as Occupational Exposure Limits, and Short-Term Exposure Limits to address the need of the agent in the workplace as well as to attempt to protect the workers. Though these regulations are in place, they may not be followed accurately and proper monitoring is difficult to establish. Even with proper application of these regulations, the long latency periods of cancers mean that there is no immediate cause and effect to exposure of a chemical so immediate action may not be taken, which may be detrimental to the workers in that field.