Occupational_Cancer

Occupational_Cancer - 1 Occupational Cancer Epidemiology...

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Unformatted text preview: 1 Occupational Cancer Epidemiology Mark Goldberg Dept. Of Medicine McGill University Goal To identify chemical & physical agents in the workplace that cause cancer in humans. 2 Difficulty How does one decide whether exposure to some agent is a cause of cancer in humans? Issues ¡ Latency : solid tumours take ~10-20 years to develop ¡ Multifactorial : > 1 exposures can cause cancer (interactions) ¡ Timing of exposures : multistage and two-stage models; can be very complicated 3 Issues (continued) ¡ Hereditary: non-sporadic cancers; functional genetic polymorphisms ¡ Cellular mechanisms : host factors and their interaction with exogenous factors likely to be important ¡ Measurement of exposure : difficult to characterize and quantify Available Data ¡ Occupational exposures ¡ Cohort ¡ Case-control ¡ Cross-sectional ¡ Ecologic ¡ Environmental exposures ¡ Similar designs as in occupational studies ¡ Toxicological data ¡ Other experimental data 4 Example – Case-Control Studies ¡ Case-control study of occupational risk factors for cancer on men (Siemiatycki, “Risk factors for cancer in the workplace”, CRC Press, 1991) 1909 1950 1979 1985 Subjects • X Time X Case (X) Control Birth years Case ident. Montreal aged 35- 70 Ê Characteristics of the study design ¡ , age 35-70, living in Montreal between 1979 & 1985 ¡ ~20 sites of cancer, confirmed histologically ¡ Small (~350) population-based series of control subjects Ê 5 ¡ Interviewer-administered questionnaire for non-occupational risk factors and lifetime occupational histories Occupational questionnaire ¢ General questionnaire about each job each subject ever had ¢ Supplemented with specific questionnaires for selected jobs (e.g. welders) 6 7 8 9 Occupational Coding ¡ Team of chemists & industrial hygienists reviewed each job history & attributed exposure to ~300 agents ¡ Coded: ¡ Lifetime occupations (as coded by job and industry titles) ¡ Lifetime exposure to ~300 agents in the workplace 10 ¡ Exposure variables ¡ Start/end dates of job; duration ¡ Concentration, coded on a 4-level ordinal scale None Low- Background exposure Medium- In between High- Handling product in concentrated form ¡ Frequency, coded on 4-level interval scale None Low- 1-5% Medium- 5-30% High- >30% 11 ¡ Route of exposure, nominal Respiratory Cutaneous Both ¡ Confidence of exposure, ordinal “Possible” “Probable” “Certain” 12 Statistical Analysis ¡ Logistic regression (unconditional) using selected sites of cancer & population controls as reference ¡ Adjusted for measured risk factors ¡ Exposure indices ¡ Duration at medium/high concentrations ¡ Cumulative = ¡ “Substantial 1 ” - conc ≥ medium (2) freq ≥ high (3) ¡ “ Substantial 2 ” - conc * freq > 3 duration > 5 y prior to 5 years before dx ∑ jobs duration * freq * conc Coding: conc= {0,…,3} freq= {0,…,3} 13...
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This note was uploaded on 01/06/2012 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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Occupational_Cancer - 1 Occupational Cancer Epidemiology...

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