Cancer%20Molecular%20Epidemiology

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Cancer Molecular Epidemiology

• Epidemiology 242
• 2009

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Numbers of Papers/Year Published with Subject
Words Molecular Epidemiology Using Pubmed Search
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Evolution of Epidemiology in History

• Systematic collection and analysis of vital
  statistics
• Defined triad of agent-host-vector for both
  infectious and chronic disease
• Refine exposure assessment such as job-exposure
  matrix, dietary and nutritional analysis
• Defined study design such as case-control and
  cohort study
• Use of the advance of statistical and
  computational capacities (MLE, Logistic
  regression, poission regression)

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Evolution of Epidemiology

• Now, it is the time to add biological variables
  (physiologic, cellular, subcellular, molecular
  levels), which can be assayed by technically
  powerful biological methods
• Molecular epidemiology is the use of these
  biological markers in epidemiology research.

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Epidemiology and Molecular Sciences Epidemiology
Molecular
Sciences

• Health effects in grouped people
• Observation and inference of association between
  variables
• Macro

• Assessment of the individual at the component
  level
• Experimental proof of cause and effects
• Micro

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Molecular Epidemiology and Traditional
Epidemiology

• These capacities provide additional tool for
  epidemiologists studying questions on etiology,
  prevention and control of diseases
• Although molecular epidemiology can be viewed as
  an evolution step of epidemiology, it generally
  dose not represent a shift in the basic paradigm
  of epidemiology

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Traditional and Molecular EpidemiologyTraditiona
l Molecular

• Association
• High exposure and single outcome
• Prevention through control of exposure is
  feasible without understanding cellular process

• Mechanisms
• Smaller and mixed exposures multicausal
• Intervention through cellular process has the
  need to understand mechanisms of the process

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Basics of Molecular Epidemiology

• The term of molecular epidemiology indicates the
  incorporation of molecular, cellular, and other
  biological measurements into epidemiologic
  studies

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Molecular Epidemiology

• studies utilizing biological markers of exposure,
  disease and susceptibility
• studies which apply current and future
  generations of biomarkers in epidemiologic
  research.

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Functional Definition of Molecular Epidemiology

• The use of biologic markers or biologic
  measurements in epidemiologic research.
  Biological markers (or biomarkers) generally
  include biochemical, molecular, genetic,
  immunologic, or physiologic signals of events in
  biologic system.

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Molecular Epidemiology

• The goal of molecular epidemiology is to
  supplement and integrate, not to replace,
  existing methods
• Molecular epidemiology can be utilized to enhance
  capacity of epidemiology to understand disease in
  terms of the interaction of the environment and
  heredity.

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Capacities of Molecular Epidemiology

• Identification of Exposure at the smaller scale
• Identification of events earlier in the nature
  history of disease
• Evaluation of gene-environment interaction
• In addition, it can be used to reduce
  misclassification, to indicate mechanisms, and
  enhance risk assessment

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Study of Black Box

• The concept of a continuum of events between
  exposure and disease provide opportunities
• To ensure that epidemiologic research has a
  biological basis for hypothesis
• To provide the analysis to test these ideas
• To generate new epidemiological methods to deal
  with new challenges

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Cancer Epidemiol Biomarkers Prev 200716(10).
October 2007
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Measurement of Biomarkers

• Biomarkers can be measured quantitatively or
  qualitatively by biochemical, immunochemical,
  cytogentic, molecular and genetic techniques.

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Materials for Biomarker Measurement

• Biomarkers can be measured in human biological
  materials including normal and tumor tissues,
  blood and urine sample, etc.. Their biological
  nature can be DNA, RNA, and protein, etc.

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Study Questions Exposure Markers

• How reliable are the exposure data obtained by
  questionnaire and what type of misclassification
  bias result?
• How are the carcinogens metabolized? What are
  the dynamics and distribution of carcinogen
  metabolization?
• What is the concentration of carcinogens in
  peripheral blood? What is the exposure level in
  the target tissue? Can we employ the exposure
  markers measured in peripheral blood to predict
  the concentrations of exposure at the target
  tissue?

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Exposure Measurements
The powerful tools of molecular biology,
analytical chemistry, and related
disciplines allow measure smaller amounts of
exposures (10-18 -10-21) Reconstruct past
exposure doses using molecular measurements
(biologic dosimetry)
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Exposure Biomarkers
Mutagenesis vol. 24,117125, 2009
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Exposure Markers DNA Adducts

• Exposure markers are a group of biomarkers, which
  can indicate the environmental exposures and can
  be measured in tumor tissues, or blood or urine
  specimens.
• The presence or concentration of specific
  environmental carcinogens or other agents can be
  measured in biological specimens, for example,
  blood levels of cotinine, polycyclic aromatic
  hydrocarbon (PAH) -DNA adducts, 4-aminobiphenyl
  (4-ABP) hemoglobin adducts.

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Exposure Markers DNA Adducts

• exposure markers measure biological effective
  dose, that is, the amount of carcinogens bound to
  DNA in the target tissue such as DNA-adducts, or
  surrogate measurements which can represent the
  exposure levels of the target tissue such as
  hemoglobin adducts

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Exposure Markers

• Aromatic Amines and 4-ABP DNA-Adducts. The human
  bladder carcinogens 2-naphtylamine and
  4-aminobiphenyl, as well as the suspected
  carcinogen o-toluidine, are present in tobacco
  and certain occupational exposures. DNA adducts
  of 4-aminobiphenyl were found in tumor samples
  from smokers indicating that this agent may
  account for some of the carcinogenicity of
  tobacco smoke

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Exposure Markers

• Polycyclic Aromatic Hydrocarbons (PAH) and PAH
  DNA-Adducts. PAHs are produced by incomplete
  combustion of organic materials and the sources
  of environmental PAH include industrial and
  domestic furnaces, gasoline and diesel engines
  and tobacco smoke. PAHs are carcinogens requiring
  metabolic activation to react with cellular
  macromolecules, the initial step in tumorigenesis

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PHIP DNA Adducts
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P32 postlabeling
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Limitations of Exposure Markers

• These markers have to be measured in biological
  materials, which requires the collection of
  biological specimens
• Some of exposure markers such as
  hemoglobin-adducts and blood level of cotinine
  only represent the current exposure status
• The costs for measurement of exposure markers are
  generally more expensive than that of
  questionnaire data.

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Study Questions Susceptibility Genes

• Which gene or enzymes are involved?
• Is there any metabolic phenotype related to the
  risk of cancer?
• Are there any high risk individuals who are
  susceptible to cancer and how can we identify
  them?

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Susceptibility Markers

• Susceptibility markers represent a group of tumor
  markers, which may make an individual susceptible
  to cancer.
• These markers may be genetically inherited or
  determined.
• They are independent of environmental exposures.

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Susceptibility Markers

• Tumor susceptibility markers such as P450s, GSTs,
  and NATs, act in enzymatic pathways related to
  metabolizing and eliminating carcinogens.

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Susceptibility Markers

• The phase I enzymes such as p450 enzyme
  superfamily metabolize exogenous or endogenous
  agents or carcinogens to intermediates, which can
  result in DNA damages and act as risk factors for
  cancer.
• The phase II enzymes such as glutathione
  S-transferase (GST) system are dealing with
  detoxification of oxygenated intermediates by
  conjugation process, acting as a protective
  factors for cancer.

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Case 1 Case 2 Case 3
Case 4 Case 5
GST T1
beta-globin
GST M1
Figure. GSTM1 and GSTT1 genotyping from buccal
cell DNA. Case 5 is null for the GSTT1 genotype.
Case 2 is null for the GSTM1 genotype
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Case 1 Case 2 Case 3 Case 4 Case 5
Case 6 Case 7 Case 8
ile/val ile/val ile/ile
val/val ile/val ile/ile
ile/val ile/ile
Figure. GSTP1 polymorphism
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14 13 12 11 10 9 8 7 6
5 4 3 2 1
PCR P450 2E1 after Using Pst1 RFLP
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Case 1 Case 2 Case 3 Case 4 Case 5
Arg/Arg Arg/Arg Pro/Pro Arg/Arg
Arg/Pro
Figure. P53 polymorphism at codon 72 from buccal
cell DNA.
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Interactions between smoking and GST M1(odds
ratios and 95 confidence intervals)
5.29 (1.81, 15.4)
2.79 (0.97, 7.99)
1.13 (0.32, 3.95)
1.00
Adjusted for age, sex, race, and level of
education
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Kingsmore, 2008
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Issues in GWAS Studies

• False positive (multiple comparison)
• False negative (very small p-value)
• Population stratification
• Gene-Environmental Interaction

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Background

• In 2006 and 2007 GWAS studies identified
  associations between SNPs in the 8q24 region and
  prostate cancer among Icelandic, Swedish,
  European American, African American, and the
  Multiethnic Cohort populations.

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Research Questions Genetic and Molecular
Alterations

• What kinds of damages do the carcinogens make,
  and is the damage specific?
• Does the DNA repair capacity affect risk and how
  can we measure it?
• Is there any gene-gene interaction and is there
  any gene-environment interaction?

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Identification of Earlier Events

• Identification of the patients at a very early
  stage - for better treatment and prognosis to
  improve the survival of cancer
• Identification of pre-malignant lesions - for
  intervention and early treatment to reduce the
  incidence of cancer

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Early Biological Response Molecular Genetic
Alterations

• Molecular genetic markers are defined as a group
  of markers which can be induced by certain
  carcinogens or by some intermediate end-point

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Early Biological Response Molecular Genetic
Alterations

• cytogenetic markers such as chromosome
  abnormalities by karyotyping
• oncogenes such as RAS family
• tumor suppressor genes such as TP53 and p16 genes.

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P53 Gene Mutations

• TP53 Mutations as DNA Fingerprints of
  Environmental Exposures. The wide range of
  involvement of TP53 in human tumors and the broad
  spectrum of mutations make this gene a good
  candidate for molecular epidemiological studies

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Case 607 Exon 8
Case 644 Exon 7
1 2 3
1 2 3
Mutant
Wild Type
Mutant
Wild Type
G A T C G A T C
G A T C G A T C
A
A
C
C
C/G
G
G
G
A
A/G
A
G
Arg
Thr
Gly
Ser
A C/G A
A/G G C
Codon 280
Codon 244
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Figure 8-1. IHC Analysis of p53, p21, and mdm2
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Case 1 Case 2 Case 3
(unmethylated) (unmethylated)
(methylated)
Figure 11. GST P1 methylation from lung cancer
tissue. (Uunmethylated, Mmethylated) Case 3 is
unmethylated.
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Age and TP53 Mutations
Age P53 No. () P53- No. () Total No. ()
lt50 6 (8.7) 11 (10.0) 17 (9.5)
50-59 16 (23.2) 18 (16.4) 34 (19.0)
60 47 (68.1) 81 (73.6) 128 (71.5)
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Gender and TP53 Mutations
Gender TP53 No () TP53- No () Total No ()
Male 47 (71.2) 89 (81.7) 136 (77.7)
Female 19 (28.8) 20 (18.4) 39 (22.3)
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Race and TP53 Mutations
Race TP53 No () TP53- No () Total No. ()
White 60 (87.0) 100 (90.9) 160 (89.4)
Non-White 9 (13.0) 10 (9.1) 19 (10.6)
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Education and TP53 Mutations
Education (years) TP53 No. () TP53- No. () Total No. ()
lt12 2 (2.9) 4 (3.6) 6 (3.4)
12-16 58 (84.1) 76 (69.1) 134 (74.9)
gt16 9 (13.0) 30 (27.3) 39 (21.8)
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TP53 Mutations in Bladder Cancer
BP changes Reported, n200 Current study
Transitions
GC ?AT 41.0 37.5
(at CpG) 14.0 12.5
AT?GC 10.0 15.0
Transversions
GC?TA 13.0 12.5
GC?CG 19.0 10.0
AT?TA 3.0 0.0
AT?CG 2.0 2.5
Deletion/Insert. 12.0 10.0
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Smoking and TP53 Mutations in Bladder Cancer
Smoking TP53 TP53- OR 95CI
No 8 24 1.00
Yes 58 83 6.27 1.29-30.2
Adjusted for age, gender, and education
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Cigarettes/day and TP53 Mutations in Bladder
Cancer
Cig/day TP53 TP53- OR 95CI
No 8 24 1.00
1-20 8 21 2.07 0.22-19.9
21-40 36 47 5.50 1.08-28.2
gt40 17 18 10.4 1.90-56.8
Trend P0.003
Adjusted for age, gender, and education
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Years of Smoking and TP53 Mutations in Bladder
Cancer
Years of smoking TP53 TP53- OR 95CI
No 8 24 1.00
1-20 5 10 5.64 0.82-38.7
21-40 42 58 6.45 1.24-33.4
gt40 14 18 6.20 1.17-32.8
Trend P0.041
Adjusted for age, gender and education
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Reduction of Misclassifications

• Better classification of exposures by using
  markers of internal and biological effective
  doses.
• More homogeneous disease grouping by using marker
  of effect such as specific mutations.
• Reduced misclassification may lead to increased
  validity and precision of point estimates

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Indication of Mechanisms

• Test association between mechanistic events in a
  defined continuum
• Knowledge of the mechanisms can guide future
  research and intervention applications

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Variability and Effect Modification

• Individual variability of susceptibility may be
  related to host factors such as genetic factors
• Effect modification can be evaluated between
  genetic susceptibility markers and exposure on
  the risk of cancer

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Enhanced Individual and Group Risk Assessment

• Providing more person-specific information
• allowing extrapolation of risk from one group to
  another, from animal species to humans, and from
  one group to individuals

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Example Smoking and Lung Cancer

• Internal Dose (ID). The amount of a xenobiotic
  substance or its metabolites found in a biologic
  medium e.g., Serum cotinine as an indicator of
  nicotine.
• Biologic Effective Dose (BED). The integration of
  exposure and effect modification by the host
  e.g., DNA adducts of PAH in lung tissue.

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Example Smoking and Lung Cancer

• Early Biologic Effect (or biological response)
  are biological or biochemical changes in target
  cells or tissues that result from the action of
  the chemical and are thought to be a step in the
  pathologic process toward disease, e.g., tumor
  suppressor gene TP53 mutations in lung cancer.

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