By : Dr. Aliraza Safaiyan M.D. Occupational Medicine Specialist
Occupational Cancer
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Introduction One of every two or three individuals in the
industrialized world will develop some type of cancer during their
lifetimes Approximately 3-10% of all human cancers are thought to
be caused by occupational exposure to carcinogens It is estimated
that approximately 20,000 cancer deaths and 40,000 new cases of
cancer each year in the U.S. are attributable to occupation
Occupational carcinogens is important because they are completely
preventablee.
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The most common cancers associated with occupational exposure:
lung and pleura bladder skin laryngeal nasal cavity leukemia throat
lymphoma soft-tissue sarcomas liver
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Related to Occupational Exposure Estimated % (USA) Type of
Cancer 6.3 13 %Lung 3 19 %Bladder 85-90% (men); 23-90% (women*)
Mesothelioma 0.8 2.8 %Leukemia 1-20% (men)Laryngeal 1.5-6%
(men)Skin Cancer (non-melanoma) 31-43% (men)Sinonasal and
nasopharyngeal 0 2.3 %Kidney 0.4-1.1 (vinyl chloride only;
men)Liver * In general, the overall attributable risk for
mesothelioma in women is 23%. However, if the woman has had "take-
home" exposure to asbestos, the risk may be around 90%. "Take-home"
exposure results from asbestos being carried home on contaminated
work clothing or other items.
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Risk of developing a particular cancer Personal characteristics
such as age, sex, and race Family history of cancer Diet and
personal habits such as cigarette smoking and alcohol consumption
The presence of certain medical conditions Exposure to
cancer-causing agents in the environment Exposure to cancer-causing
agents in the workplace
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Stages in tumor development Initiation (irreversible changes in
DNA) Promotion (facilitate tumor development) Progression
(development to malignant tumor & metastases)
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Examples (PAH) & (croton oil) in skin cancers in mice
(Nitrosamine) & (PCB) in liver tumor in mice Complete
carcinogens (cigarette smoke)
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Induction-Latency period 3 - 5 years for radiation or toxin
induced Leukemia 20 - 40 or more asbestos-induced Mesothelioma
Solid tumors about 10 12 years For most tumors about 12 - 25
years
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Initiators VS Promoters Genotoxic Carcinogenic alone Covalently
bind to DNA (irreversible) Single exposure (may be) Not genotoxic
Act after initiation Act by cellular proliferation (may be
reversible) Repeated exposure required InitiatorsPromoters
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Prevention Elimination: The most effective means is to ban the
carcinogen. (asbestos). Substitution Alternatively, a carcinogenic
substance may be substituted with one that is not carcinogenic, or
is less hazardous. Engineering controls (expensive, but effective
means) for example, ventilation, enclosure or partial enclosure,
isolation Administrative controls : job rotation Personal
protective equipment (PPE) is the least efficient way of
controlling hazardous exposures.
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International Agency of Research on Cancers IARC
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the IARC classifications Group 1: The agent is carcinogenic to
humans. sufficient evidence of carcinogenicity in humans. Group 2A:
The agent is probably carcinogenic to humans. limited evidence of
carcinogenicity in humans and sufficient evidence in experimental
animals. Group 2B: The agent is possibly carcinogenic to humans.
limited evidence of carcinogenicity in humans and less than
sufficient evidence in experimental animals. Group 3: The agent is
not classifiable as to its carcinogenicity to humans. the evidence
of carcinogenicity is inadequate in humans and inadequate or
limited in experimental animals. Group 4: The agent is probably not
carcinogenic to humans. there is evidence suggesting lack of
carcinogenicity in humans and in experimental animals.
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IARC Evaluations Dimensions and Groups 14 Types of evidence
Human Animal Other - mutagenicity - genotoxicity - metabolism -
etc. Group 1Carcinogenic to humans 2AProbably carcinogenic to
humans 2BPossibly carcinogenic to humans 3Not classifiable 4Not
carcinogenic to humans
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the IARC classifications Group 1 : 63 agents, 13 mixtures and
15 exposure circumstances. This includes a number of occupations
(eg painter, cabinet maker) as well as different chemicals used
primarily in occupational circumstances. group 2A : 31 agents and 3
exposure circumstances are classified. Not all these agents are
occupational carcinogens and a review of the IARC classifications
found that 28 agents were definite occupational carcinogens, and a
further27 were probable occupational carcinogens
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28 definite human occupational carcinogens (IARC group 1); 27
probable human occupational carcinogens (IARC group 2A); 113
possible human occupational carcinogens (IARC group 2B); and 18
occupations and industries that possibly, probably or definitely
entail excess risk of cancer (IARC groups 1, 2A and 2B).
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United States Department of Health and Human Services Report on
Carcinogens (RoC) Substances on the RoC are classified into one of
two groups: Known to be human carcinogen. Reasonably anticipated to
be human carcinogenic. The 10th RoC classifies 52 substances into
the known carcinogens group, and a further 176 substances into the
reasonably anticipated carcinogens group.
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United States Environmental Protection Authority (EPA) Agents
can be classified as: Carcinogenic to humans: when there is
convincing epidemiologic evidence demonstrating causality between
human exposure and cancer. Likely to be carcinogenic to humans:
when the available data are adequate to demonstrate carcinogenic
potential to humans. Suggestive evidence of carcinogenic potential:
when the evidence from human or animal data is suggestive of
carcinogenicity but is not sufficient for a stronger conclusion.
Inadequate information to assess carcinogenic potential. Not likely
to be carcinogenic to humans. the EPA are much more conservative
than any other organization. They have only classified three
substances (arsenic, benzene, chromium IV) as carcinogenic to
humans, and a further 102 as likely or probable carcinogens. They
have not evaluated any form of asbestos.
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The most Important Occupational cancers
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Lung cancer (Exposures) Tobacco smoking is responsible for
nearly 90% of all lung cancers. Second-hand smoke Byproducts of
fossil fuel Air pollution Insufficient consumption of fruits and
vegetables High doses of ionizing radiation Asbestos Radon
chloromethyl ethers Polycyclic aromatic hydrocarbons Inorganic
arsenic Chromium Nickel Mustard Gas Generalworkplaces
Mesothelioma (prevention) OSHA PEL (1970) :5 Fiber/cm3 (1986):2
fiber/cm3 now: 0.1 fiber/cm3 Asbestos ban : since 1989 by EPA
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Asbestos Ban (1989)
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Bladder cancer (exposure) The most important risk factor is
cigarette smoking. Heavy coffee consumption (Possible risk factors
) Bladder infection with schistosoma Cyclophosphamide Long-term use
of pain killers containing phenacetin, Urinary tract infections or
low urine flow Genetic factors Benzidine 2-naphthylamine
Occupations in the dye, leather or rubber industry Chlornaphazine 4
chlorotoluidine Phenacetine Generalworkplace
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Bladder cancer (findings) Hematuria (Painless, gross,
intermittent) 80% Vesical irritability alone 20% In advance cases:
Anemia Uremia Leg edema Urinary cytology (in up to 75% of patients
is positive) Ultrasonography Excretory urography Cystoscopy &
biopsy (definitive diagnosis) Symptoms & signsParaclinics
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Bladder cancer (prevention) Avoidance of exposure Medical
monitoring : Urinary cytology (75% Sen. 99.9 Spes.)
Immunocytology