Online Data Supplement
Appendix: additional detailed methods
1. Diagnostic criteria of COPD and lung cancer
Lung function was tested with the EasyOne Spirometer (EasyOne Spirometer, ndd
Medizintechnik AG, Switzerland). Subjects with forced expiratory volume in one second (FEV1)
to forced vital capacity (FVC) <70% after inhalation of 400μg salbutamol and with some chronic
airway symptoms, such as chronic cough, dyspnea, sputum production or wheezing were
identified as COPD cases. Lung cancer patients or control subjects with physician-diagnosed
COPD by the Spirometry test at least one year before lung cancer diagnosis or control
recruitment were defined to have pre-existing COPD. The diagnosis of COPD was according to
the global initiative for chronic obstructive lung disease. Lung cancer was diagnosed according to
standard clinical criteria with pathologic confirmation from surgery, biopsy, or cytology samples.
Main analyses included all primary lung cancer cases regardless of histological types.
2. COPD Samples collection
All normal pulmonary function controls were age (±5 years) and sex frequency-matched with
cases. In the discovery set, 697 COPD cases from southern Chinese were screened and recruited
during a community cross-sectional survey of COPD in three communities (Liwan, Xicun and
Zhanqian communities) of Guangzhou city between February 2002 and June 2008 with a
response rate of about 83%, and 328 cases were recruited from municipal hospitals in Guangzhou
(the Guangzhou Chest Hospital, The third Affiliated Hospital of Guangzhou Medical University,
the third Affiliated Hospital of Sun Yat-sen University) between December 2007 and June 2010
with a 91% response rate; 1061 normal lung function controls (FEV1/ FVC > 70%) were
randomly picked from individuals participating in the community cross-sectional survey. In the
validation set, 486 COPD cases from eastern Chinese were recruited from the second Affiliate
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Hospital of Soochow University (Suzhou) with a response rate of 83% during the July 2009 to
June 2011; 616 normal pulmonary function controls were randomly selected from a database
consisting of 3,500 individuals based on a physical examination with an 81% response rate. All
participants were genetically unrelated ethnic Han Chinese and none had blood transfusions in
the last 6 months.
3. Lung cancer samples collection
All cancer-free controls were age (±5 years) and sex frequency-matched with lung cancer cases.
1056 histopathologically confirmed cases with primary lung cancer were recruited at four urban
hospitals (i.e., the First Hospital, the Second Hospital, and the Tumor Hospitals affiliated to
Guangzhou Medical University as well as the Guangzhou Chest Hospital) and at one suburb
hospital (i.e., PanYu People’s Hospital) of Guangzhou city from March 2007 to March 2009, with
an overall response rate of about 95%, and 1056 age (±5 years) and sex frequency-matched
cancer-free controls were randomly picked from about 10,000 participants of healthy check-up
program conducted in Guangzhou City during the same period with a response rate of 84%. An
eastern Chinese population was used to validate the findings with 503 newly diagnosed lung
cancer patients who were continually recruited from March 2008 to May 2010 at the first
Affiliate Hospital of Soochow University (Suzhou) with a response rate of 87% and 623 age (±5
years) and sex frequency-matched controls who were selected from a database consisting of 3500
individuals based on a physical examination with a 81% response rate. All participants were
genetically unrelated ethnic Han Chinese and none had blood transfusions in the last 6 months.
4. Definitions of studied factors
Those participants who had smoked <100 cigarettes in their lifetime were defined as never
smokers; otherwise, they were classified as ever smokers. Number of pack-years smoked was
calculated by packs smoked per day × years as a smoker. Low pack-year smoked referred to
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someone who had less than or equal to 5 pack-years of smoking, moderate pack-years smoked
referred to those had more than 5 and less than or equal to 20 pack-years of smoking, while high
pack-years smoked referred to those had more than 20 pack-years of smoking. Similarly,
participants who had consumed alcoholic beverages at least once a week for ≥1 year were defined
as ever drinkers, and the remainders as never drinkers. Individuals have an “often” frequency of
cooking times refer to those who cook more than 5 times in one week, and a “seldom” frequency
mean those who cook but less than 5 times in one week.
5. Test of mediation effect
The statistical protocol was orderly performed to obtain essential parameters abiding with the
excel procedure ‘Spreadsheet’ as suggested on the website
(http://www.nrhpsych.com/mediation/logmed.html), and the Sobel test was used to test the
significance of mediation effect by using the website tool (Interactive calculation tool:
http://quantpsy.org/sobel/sobel.htm). First, by using the unconditional Logistical regression
model with adjustments for four covariates (i.e., age, sex, BMI and education level), two
regression coefficients (defined as b and c’) was obtained by regressing the outcome (i.e., lung
cancer) on COPD and risk factors if no significant interaction was observed between risk factors
and COPD; or three coefficients (similarly defined as b, c’ and d) was obtained by regressing the
outcome on COPD, risk factors and COPD× risk factors if significant interactions were existed
between risk factors and COPD. Secondly, by using an extended inverse-propensity-weighted
(IPW) regression approach as suggested by Richardson et, al. and Wang et, al. (1, 2), one
coefficient (defined as a) was calculated by regressing COPD on risk factors. In the process of the
calculation, the cases were weighted as 1 and the controls were weighted as a ratio, [(N1× (1 −
fD))/(N0×fD). Among the ratio, N1 and N0 were the number of cases and controls, and fD was the
prevalence of lung cancer in total population. In the current study, the controls were weighted as
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17321[i.e., 559× (1-0.0005357)/(1679×0.0005357)]. Afterwards, all above coefficients were turn
into be comparable (defined as α, β, τ′ and θ) by multiplying each coefficient by the standard
deviation (SD) of the predictor variable and then dividing by the SD of the outcome variable as
suggested by MacKinnon and Dwyer (3). That was, α = a × SD(risk factor)/SD(COPD), β = b ×
SD(COPD)/SD(lung cancer), τ′ = c’ × SD(risk factor)/SD(lung cancer), and θ = d× SD(risk factor
×COPD) / SD(lung cancer). Finally, if there was no significant interaction between risk factors
and COPD, the direct effect of factors on lung cancer risk was equal to τ′, and the indirect effect
of factors on lung cancer risk through COPD was equal to αβ. The total effect τ = τ′ + αβ, and the
proportion for mediation effect was αβ/τ. When there were significant interactions between risk
factors and COPD, the direct effect was τ′ +θ; the indirect effect was αβ + αθ. The total effect τ
=τ′ +θ +αβ + αθ, and the proportion for mediation effect was (αβ+ αθ)/τ.
References:
1.
Richardson DB, Rzehak P, Klenk J, Weiland SK. (2007) Analyses of case-control data for
additional outcomes. Epidemiology. 18: 441-5.
2.
Wang J, Shete S. (2011) Estimation of odds ratios of genetic variants for the secondary
phenotypes associated with primary diseases. Genet Epidemiol. 35: 190-200.
3.
MacKinnon DP, Dwyer JH. (1993) Estimating mediated effects in prevention studies.
Evaluation Review. 17: 144-58.
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