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Jack Siemiatycki

Publications and source records attributed to Jack Siemiatycki.

At least 19 recordsLinked to original sources
PubMed2006

Modelling smoking history using a comprehensive smoking index: application to lung cancer.

The mathematical representation of smoking history is an important tool in analysis of epidemiological and clinical data. Hoffmann and colleagues recently proposed a single aggregate measure of smoking exposure that incorporates intensity, duration, and time since cessation. This comprehensive smoking index (CSI), which may be incorporated in any regression model, depends on a half-life (tau) and a lag (delta) parameters that have to be fixed a priori, or estimated by maximizing the fit. The CSI has not previously been used for analysis of cancer data. Following some preliminary results on smoking and lung cancer, the authors proposed a new version of the CSI for lung cancer. The aim of this study was to investigate the performance of the original and the new versions of the CSI in the analysis of three data sets from two case-control studies of lung cancer undertaken in Montreal, in 1979-1985 in males, and in 1996-2000 in both males and females. The estimates of tau and delta for both versions of the CSI were similar across data sets. The new version of the CSI fitted the three data sets systematically although moderately better than the original version, and at least as well as other representations of lifetime smoking history that used separate variables for time since cessation and cumulative amount of cigarettes smoked. The results suggest that the CSI may be an attractive and parsimonious alternative to conventional modelling of different aspects of smoking history for lung cancer.

Adult↗
PubMed2006

Risk of lung cancer from residential heating and cooking fuels in Montreal, Canada.

Among the major sources of indoor air pollution are combustion by-products from heating and cooking. Concern is increasing that use of polluting heating and cooking sources can increase cancer risk. In Canada, most cooking and heating currently relies on electricity or natural gas, but, in the past, and still in some areas, coal and wood stoves were used for heating and gas and wood for cooking. In the course of a case-control study of lung cancer carried out in Montreal in 1996-2001, the authors collected information on subjects' lifetime exposure to such sources of domestic pollution by means of a personal interview with the subject or a next-of-kin proxy. Questionnaires were completed for 739 male cases, 925 male controls, 466 female cases, and 616 female controls. Odds ratios were computed in relation to a few indices of exposure to traditional heating and cooking sources, adjusting for a number of covariates, including smoking. Among men, there was no indication of excess risks. Among women, the odds ratio for those exposed to both traditional heating and cooking sources was 2.5 (95% confidence interval: 1.5, 3.6; n = 253). The findings for women suggest the need for research dedicated to exploring this association, with particular emphasis on improved exposure assessment.

Adenocarcinoma↗
PubMed2006

Exposure to diesel and gasoline engine emissions and the risk of lung cancer.

Pollution from motor vehicles constitutes a major environmental health problem. The present paper describes associations between diesel and gasoline engine emissions and lung cancer, as evidenced in a 1979-1985 population-based case-control study in Montreal, Canada. Cases were 857 male lung cancer patients. Controls were 533 population controls and 1,349 patients with other cancer types. Subjects were interviewed to obtain a detailed lifetime job history and relevant data on potential confounders. Industrial hygienists translated each job description into indices of exposure to several agents, including engine emissions. There was no evidence of excess risks of lung cancer with exposure to gasoline exhaust. For diesel engine emissions, results differed by control group. When cancer controls were considered, there was no excess risk. When population controls were studied, the odds ratios, after adjustments for potential confounders, were 1.2 (95% confidence interval: 0.8, 1.8) for any exposure and 1.6 (95% confidence interval: 0.9, 2.8) for substantial exposure. Confidence intervals between risk estimates derived from the two control groups overlapped considerably. These results provide some limited support for the hypothesis of an excess lung cancer risk due to diesel exhaust but no support for an increase in risk due to gasoline exhaust.

Adult↗
PubMed2006

Risk of lung cancer following nonmalignant respiratory conditions: evidence from two case-control studies in Montreal, Canada.

There has been conflicting evidence concerning possible associations between several nonmalignant respiratory diseases and subsequent risk of lung cancer. In the context of two large population based case-control studies of lung cancer carried out in Montreal, we were able to study the possible relationships between a previous history of lung disease and subsequent risk of lung cancer. Interviews for Study I were conducted in 1979-1986 (755 cases and 512 controls) and included questions on asthma and tuberculosis. Interviews for Study II were conducted in 1996-2001 (1205 cases and 1541 controls) and included questions on asthma, tuberculosis, emphysema, and pneumonia. Lung cancer risk was analysed in relation to each condition, adjusting for several potential confounders, including smoking in a three-variable parametrization. To avoid any possible confusion between the respiratory conditions and early symptoms of lung cancer, conditions occurring in the 3 years before diagnosis of cancer were discounted. For asthma there was no evidence of an association. For TB the evidence was inconsistent between Study I and Study II. For both pneumonia and emphysema, there were significantly elevated odds ratios, with point estimates in the range of 1.6-2.4. Our results support the hypothesis that some nonmalignant respiratory diseases may be independent risk factors for lung cancer.

Adult↗
PubMed2006

Diabetes mellitus and cancer risk in a population-based case-control study among men from Montreal, Canada.

Diabetics may have a higher risk of cancer, notably liver and pancreatic cancers. Evidence about other cancer types remains sparse. The authors examined potential associations between diabetes and several types of cancer in a large multicancer case-control project carried out in Montreal, Canada, in the 1980s. This report, based on 3,107 male cancer cases and 509 population controls, uses information on diabetes and several covariates collected by interview. Adjusted odds ratios (ORs) and 95% confidence intervals (CI) were estimated for the associations between diabetes and each of 12 cancer types. Risks of pancreatic and liver cancers were increased among diabetics: adjusted ORs were 2.1 (95% CI: 1.0, 4.3) for pancreatic and 3.1 (95% CI: 1.1, 8.8) for liver cancer. The increased risk of pancreatic cancer was completely restricted to those with recent onset of diabetes; this was likely a manifestation of reverse causality. Conversely, the increased risk of liver cancer was independent of the interval between diabetes and cancer diagnoses. No associations were observed with melanoma, non-Hodgkin's lymphoma, cancers of the esophagus, stomach, colon, rectum, lung, prostate, bladder and kidney. In conclusion, diabetes was associated with an increased risk of liver cancer among men, but with no other cancer type including pancreatic cancer.

Adult↗
PubMed2006

Consumption of alcoholic beverages and risk of lung cancer: results from two case-control studies in Montreal, Canada.

OBJECTIVE: To investigate the association between consumption of alcoholic beverages and lung cancer risk. METHODS: Data were collected in two population-based case-control studies, conducted in Montreal (Study I--mid-1980s and Study II--mid-1990s). Study I included 699 cases and 507 controls, all males; Study II included 1094 cases and 1468 controls, males and females. In each study group (Study I men, Study II men and Study II women) odds ratios (OR) were estimated for the associations between beer, wine or spirits consumption and lung cancer, while carefully adjusting for smoking and other covariates. The reference category included abstainers and occasional drinkers. RESULTS: For Study I men, lung cancer risk increased with the average number of beers/week consumed (for 1-6 beers/week: OR=1.2, 95% confidence interval (CI): 0.9-1.7; for >or=7 beers/week: OR=1.5, 95% CI: 1.1-2.1). For Study II men, beer consumption appeared harmful only among subjects with low fruit and vegetable consumption. In Study II, wine consumers had low lung cancer risk, particularly those reporting 1-6 glasses/week (women: OR=0.3, 95% CI: 0.2-0.4; men: OR=0.6, 95% CI: 0.4-0.8). CONCLUSIONS: Beer consumption increased lung cancer risk, particularly so among men who had relatively low fruit and vegetable consumption. Moderate wine drinkers had decreased lung cancer risk.

Alcohol Drinking↗
PubMed2005

Maternal exposure to occupational solvents and childhood leukemia.

Many organic solvents are considered probable carcinogens. We carried out a population-based case-control study including 790 incident cases of childhood acute lymphoblastic leukemia and as many healthy controls, matched on age and sex. Maternal occupational exposure to solvents before and during pregnancy was estimated using the expert method, which involves chemists coding each individual's job for specific contaminants. Home exposure to solvents was also evaluated. The frequency of exposure to specific agents or mixtures was generally low. Results were generally similar for the period ranging from 2 years before pregnancy up to birth and for the pregnancy period alone. For the former period, the odds ratio (OR), adjusted for maternal age and sex, for any exposure to all solvents together was 1.11 [95% confidence interval (CI), 0.88-1.40]. Increased risks were observed for specific exposures, such as to 1,1,1-trichloroethane (OR = 7.55; 95% CI, 0.92-61.97), toluene (OR = 1.88; 95% CI, 1.01-3.47), and mineral spirits (OR = 1.82; 95% CI, 1.05-3.14). There were stronger indications of moderately increased risks associated with exposure to alkanes (C5-C17; OR = 1.78; 95% CI, 1.11-2.86) and mononuclear aromatic hydrocarbons (OR = 1.64; 95% CI, 1.12-2.41). Risk did not increase with increasing exposure, except for alkanes, where a significant trend (p = 0.04) was observed. Home exposure was not associated with increased risk. Using an elaborate exposure coding method, this study shows that maternal exposure to solvents in the workplace does not seem to play a major role in childhood leukemia.

Adolescent↗
PubMed2004

Applying new biotechnologies to the study of occupational cancer--a workshop summary.

As high-throughput technologies in genomics, transcriptomics, and proteomics evolve, questions arise about their use in the assessment of occupational cancers. To address these questions, the National Institute for Occupational Safety and Health, the National Cancer Institute, the National Institute of Environmental Health Sciences, and the American Chemistry Council sponsored a workshop 8-9 May 2002 in Washington, DC. The workshop brought together 80 international specialists whose objective was to identify the means for best exploiting new technologies to enhance methods for laboratory investigation, epidemiologic evaluation, risk assessment, and prevention of occupational cancer. The workshop focused on identifying and interpreting markers for early biologic effect and inherited modifiers of risk.

Biomarkers↗
PubMed2004

Listing occupational carcinogens.

The occupational environment has been a most fruitful one for investigating the etiology of human cancer. Many recognized human carcinogens are occupational carcinogens. There is a large volume of epidemiologic and experimental data concerning cancer risks in different work environments. It is important to synthesize this information for both scientific and public health purposes. Various organizations and individuals have published lists of occupational carcinogens. However, such lists have been limited by unclear criteria for which recognized carcinogens should be considered occupational carcinogens, and by inconsistent and incomplete information on the occupations and industries in which the carcinogenic substances may be found and on their target sites of cancer. Based largely on the evaluations published by the International Agency for Research on Cancer, and augmented with additional information, the present article represents an attempt to summarize, in tabular form, current knowledge on occupational carcinogens, the occupations and industries in which they are found, and their target organs. We have considered 28 agents as definite occupational carcinogens, 27 agents as probable occupational carcinogens, and 113 agents as possible occupational carcinogens. These tables should be useful for regulatory or preventive purposes and for scientific purposes in research priority setting and in understanding carcinogenesis.

Carcinogens↗
PubMed2003

Evaluation of Cox's model and logistic regression for matched case-control data with time-dependent covariates: a simulation study.

Case-control studies are typically analysed using the conventional logistic model, which does not directly account for changes in the covariate values over time. Yet, many exposures may vary over time. The most natural alternative to handle such exposures would be to use the Cox model with time-dependent covariates. However, its application to case-control data opens the question of how to manipulate the risk sets. Through a simulation study, we investigate how the accuracy of the estimates of Cox's model depends on the operational definition of risk sets and/or on some aspects of the time-varying exposure. We also assess the estimates obtained from conventional logistic regression. The lifetime experience of a hypothetical population is first generated, and a matched case-control study is then simulated from this population. We control the frequency, the age at initiation, and the total duration of exposure, as well as the strengths of their effects. All models considered include a fixed-in-time covariate and one or two time-dependent covariate(s): the indicator of current exposure and/or the exposure duration. Simulation results show that none of the models always performs well. The discrepancies between the odds ratios yielded by logistic regression and the 'true' hazard ratio depend on both the type of the covariate and the strength of its effect. In addition, it seems that logistic regression has difficulty separating the effects of inter-correlated time-dependent covariates. By contrast, each of the two versions of Cox's model systematically induces either a serious under-estimation or a moderate over-estimation bias. The magnitude of the latter bias is proportional to the true effect, suggesting that an improved manipulation of the risk sets may eliminate, or at least reduce, the bias.

Canada↗
PubMed2003

Validation of expert assessment of occupational exposures.

BACKGROUND: Assessment by experts may be the best method available for retrospective occupational exposure measurement in community-based studies. This study was undertaken to examine the validity of occupational exposure assessment by comparing the ratings of experienced raters with previously recorded industrial hygiene measurements. METHODS: We obtained 50 measurements from industrial hygiene records, covering a variety of jobs and substances and created 47 job descriptions around these measurements. Three raters were asked to assess exposure to a checklist of 19 substances (including those substances which had been measured). We estimated the sensitivity of the raters in correctly detecting those substances known to have been present. RESULTS: Using a liberal criterion for the ratings, the average sensitivity among the raters was 90%. Using a more stringent criterion, the average sensitivity was 73%. Among substances coded as present, the raters were quite accurate in rating the relative concentration and frequency of exposure. CONCLUSIONS: This trial demonstrated that a team of experienced raters could successfully characterize jobs in which important exposures occurred.

Air Pollutants, Occupational↗
PubMed2002

Modeling smoking history: a comparison of different approaches.

The impact of cigarette smoking on various diseases is studied frequently in epidemiology. However, there is no consensus on how to model different aspects of smoking history. The aim of this investigation was to elucidate the impact of several decisions that must be made when modeling smoking variables. The authors used data on lung cancer from a case-control study undertaken in Montreal, Quebec, Canada, in 1979-1985. The roles of smoking status, intensity, duration, cigarette-years, age at initiation, and time since cessation were investigated using time-dependent variables in an adaptation of Cox's model to case-control data. The authors reached four conclusions. 1) The estimated hazard ratios for current and ex-smokers depend strongly on how long subjects are required to not have smoked to be considered "ex-smokers." 2) When the aim is to estimate the effect of continuous smoking variables, a simple approach can be used (and is proposed) to separate the qualitative difference between never and ever smokers from the quantitative effect of smoking. 3) Using intensity and duration as separate variables may lead to a better model fit than using their product (cigarette-years). 4) When estimating the effects of time since cessation or age at initiation, it is still useful to use cigarette-years, because it reduces multicollinearity.

Case-Control Studies↗
PubMed2002

Effects of alcohol consumption on the risk of colorectal cancer among men by anatomical subsite (Canada).

OBJECTIVE: To estimate the effects of alcohol consumption on the risk of colorectal cancer according to anatomical subsite. METHODS: Between 1979 and 1985 a population-based case-control study of cancer at multiple sites was carried out in Montreal. This analysis was restricted to the 585 cases with adenocarcinoma of the large bowel, aged 35-70 years, who underwent face-to-face interviews. Controls (n = 500) were selected either from electoral lists or by random-digit dialing and were frequency-matched to the cases on age. Polytomous logistic regression was used to estimate the risk of cancer of the proximal colon, distal colon, and rectum in relation to the consumption of alcoholic beverages. RESULTS: Daily consumption of alcohol of any type was associated with increased risks of cancer of the distal colon [odds ratio (OR)= 2.3; 95% confidence interval (CI) 1.4-3.7] and the rectum (OR = 1.6; 95% Cl 1.0-2.6), but not with an increased risk of cancer of the proximal colon (OR = 1.0; 95% CI: 0.6-1.7). When type of beverage was considered, beer showed strong associations with cancer at all three subsites (ORs among the heaviest drinkers ranging from 1.8 to 2.4), spirits showed weaker associations with cancer at all three subsites (ORs ranging from 1.4 to 1.6), and wine showed null associations. CONCLUSIONS: The results are consistent with the hypothesis that consumption of alcoholic beverages increases the risk of colorectal cancer. The evidence is strongest for effects on the distal colon and rectum, and, among the three types of beverage, it most strongly implicates beer.

Adult↗
PubMedDate not supplied

Overview of the reanalysis of the Harvard Six Cities Study and American Cancer Society Study of Particulate Air Pollution and Mortality.

This article provides an overview of the Reanalysis Study of the Harvard Six Cities and the American Cancer Society (ACS) studies of particulate air pollution and mortality. The previous findings of the studies have been subject to debate. In response, a reanalysis team, comprised of Canadian and American researchers, was invited to participate in an independent reanalysis project to address the concerns. Phase I of the reanalysis involved the design of data audits to determine whether each study conformed to the consistency and accuracy of their data. Phase II of the reanalysis involved conducting a series of comprehensive analyses using alternative statistical methods. Alternative models were also used to identify covariates that may confound or modify the association of particulate air pollution as well as identify sensitive population subgroups. The audit demonstrated that the data in the original analyses were of high quality, as were the risk estimates reported by the original investigators. The sensitivity analysis illustrated that the mortality risk estimates reported in both studies were found to be robust against alternative Cox models. Detailed investigation of the covariate effects found a significant modifying effect of education and a relative risk of mortality associated with fine particles and declining education levels. The study team applied spatial analytic methods to the ACS data, resulting in various levels of spatial autocorrelations supporting the reported association for fine particles mortality of the original investigators as well as demonstrating a significant association between sulfur dioxide and mortality. Collectively, our reanalysis suggest that mortality may be attributable to more than one component of the complex mixture of ambient air pollutants for U.S. urban areas.

Air↗