Lung cancer and women: results of a French case-control study

Systematic review with meta-analysis of the epidemiological evidence in the 1900s relating smoking to lung cancer

BACKGROUND

Smoking is a known lung cancer cause, but no detailed quantitative systematic review exists. We summarize evidence for various indices.

METHODS

Papers published before 2000 describing epidemiological studies involving 100+ lung cancer cases were obtained from Medline and other sources. Studies were classified as principal, or subsidiary where cases overlapped with principal studies. Data were extracted on design, exposures, histological types and confounder adjustment. RRs/ORs and 95% CIs were extracted for ever, current and ex smoking of cigarettes, pipes and cigars and indices of cigarette type and dose-response. Meta-analyses and meta-regressions investigated how relationships varied by study and RR characteristics, mainly for outcomes exactly or closely equivalent to all lung cancer, squamous cell carcinoma ("squamous") and adenocarcinoma ("adeno").

RESULTS

287 studies (20 subsidiary) were identified. Although RR estimates were markedly heterogeneous, the meta-analyses demonstrated a relationship of smoking with lung cancer risk, clearly seen for ever smoking (random-effects RR 5.50, CI 5.07-5.96) current smoking (8.43, 7.63-9.31), ex smoking (4.30, 3.93-4.71) and pipe/cigar only smoking (2.92, 2.38-3.57). It was stronger for squamous (current smoking RR 16.91, 13.14-21.76) than adeno (4.21, 3.32-5.34), and evident in both sexes (RRs somewhat higher in males), all continents (RRs highest for North America and lowest for Asia, particularly China), and both study types (RRs higher for prospective studies). Relationships were somewhat stronger in later starting and larger studies. RR estimates were similar in cigarette only and mixed smokers, and similar in smokers of pipes/cigars only, pipes only and cigars only. Exceptionally no increase in adeno risk was seen for pipe/cigar only smokers (0.93, 0.62-1.40). RRs were unrelated to mentholation, and higher for non-filter and handrolled cigarettes. RRs increased with amount smoked, duration, earlier starting age, tar level and fraction smoked and decreased with time quit. Relationships were strongest for small and squamous cell, intermediate for large cell and weakest for adenocarcinoma. Covariate-adjustment little affected RR estimates.

CONCLUSIONS

The association of lung cancer with smoking is strong, evident for all lung cancer types, dose-related and insensitive to covariate-adjustment. This emphasises the causal nature of the relationship. Our results quantify the relationships more precisely than previously.

Indoor radon and lung cancer in France

BACKGROUND

Several case-control studies have indicated an increased risk of lung cancer linked to indoor radon exposure; others have not supported this hypothesis, partly because of a lack of statistical power. As part of a large European project, a hospital-based case-control study was carried out in 4 areas in France with relatively high radon levels.

METHODS

Radon concentrations were measured in dwellings that had been occupied by the study subjects during the 5- to 30-year period before the interview. Measurements of radon concentrations were performed during a 6-month period using 2 Kodalpha LR 115 detectors (Dosirad, France), 1 in the living room and 1 in the bedroom. We examined lung cancer risk in relation to indoor radon exposure after adjustment for age, sex, region, cigarette smoking, and occupational exposure.

RESULTS

We included in the analysis 486 cases and 984 controls with radon measures in at least 1 dwelling. When lung cancer risk was examined in relation to the time-weighted average radon concentration during the 5- to 30-year period, the estimated relative risks (with 95% confidence intervals) were: 0.85 (0.59-1.22), 1.19 (0.81-1.77), 1.04 (0.64-1.67), and 1.11 (0.59-2.09) for categories 50-100, 100-200, 200-400, and 400+ becquerels per cubic meter (Bq/m), respectively (reference <50 Bq/m). The estimated relative risk per 100 Bq/m was 1.04 (0.99-1.11) for all subjects and 1.07 (1.00-1.14) for subjects with complete measurements.

CONCLUSIONS

Our results support the presence of a small excess lung cancer risk associated with indoor radon exposure after precise adjustment on smoking. They are in agreement with results from some other indoor radon case-control studies and with extrapolations from studies of underground miners.

Does increased cigarette consumption nullify any reduction in lung cancer risk associated with low-tar filter cigarettes?

Epidemiological data suggest that smoking filter and lower tar cigarettes is associated with less lung cancer risk than is smoking plain and higher tar cigarettes. A recent National Cancer Institute monograph claimed these apparent benefits of lower delivery products may be illusory if relative risks are adjusted for daily consumption, and switching leads to "compensation" for reduced nicotine intake by increasing numbers of cigarettes smoked. To investigate this, we compared relative risks unadjusted and adjusted for daily cigarette consumption. Overall estimates of the filter/plain relative risk, using random-effects meta-analysis, were 0.61 (95%confidence interval 0.54 to 0.70) for unadjusted data and 0.66 (0.58 to 0.76) for adjusted data. The lower tar/higher tar relative risk was estimated as 0.60 (0.45 to 0.81) for unadjusted data and 0.73 (0.64 to 0.83) for adjusted data. The risk reductions were clearly seen regardless of gender, study location, period, or design, and when only studies providing both unadjusted and adjusted estimates were considered. Whether or not relative risk estimates are adjusted for cigarette consumption is not crucial to the conclusion of a clear advantage to filter cigarettes and tar reduction. Data on "compensation" for amount smoked were reviewed and any increase following switching to reduced-tar-yield cigarettes was shown to be quite small. Other biases in the epidemiology are also discussed, and we conclude that the apparent advantage to reduced-tar-delivery products is real and likely to be a marked underestimate of the reduction in lung cancer risk from lifetime smoking of low-tar cigarettes.

A flexible modeling approach to estimating the component effects of smoking behavior on lung cancer

OBJECTIVE

Despite the established causal association between cigarette smoking and lung cancer, the relative contributions of age started, duration, years since quitting, and daily amount smoked have not been well characterized. We estimated the contribution of each of these aspects of smoking behavior.

STUDY DESIGN AND SETTING

A case-control study was conducted in Montreal on the etiology of lung cancer. There were 640 cases and 938 control subjects for whom lifetime smoking histories were collected. We used generalized additive models, incorporating cubic smoothing splines to model nonlinear effects of various smoking variables. We adopted a multistep approach to deal with the multicollinearity among time-related variables.

RESULTS

The main findings are that (1) risk increases independently by daily amount and by duration; (2) among current smokers, lung cancer risk doubles for every 10 cigarettes per day up to 30 to 40 cigarettes per day and tails off thereafter; (3) among ex-smokers, the odds ratio decreases with increasing time since quitting, the rate of decrease being sharper among heavy smokers than among light smokers; and (4) absolute risks demonstrate the dramatic public health benefits of long-term smoking cessation.

CONCLUSION

Our results reinforce some previous findings on this issue.

Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8

OBJECTIVE

To assess the risk of lung cancer in smokers of medium tar filter cigarettes compared with smokers of low tar and very low tar filter cigarettes.

DESIGN

Analysis of the association between the tar rating of the brand of cigarette smoked in 1982 and mortality from lung cancer over the next six years. Multivariate proportional hazards analyses used to assess hazard ratios, with adjustment for age at enrollment, race, educational level, marital status, blue collar employment, occupational exposure to asbestos, intake of vegetables, citrus fruits, and vitamins, and, in analyses of current and former smokers, for age when they started to smoke and number of cigarettes smoked per day.

SETTING

Cancer prevention study II (CPS-II).

PARTICIPANTS

364 239 men and 576 535 women, aged > or = 30 years, who had either never smoked, were former smokers, or were currently smoking a specific brand of cigarette when they were enrolled in the cancer prevention study.

MAIN OUTCOME MEASURE

Death from primary cancer of the lung among participants who had never smoked, former smokers, smokers of very low tar (< or = 7 mg tar/cigarette) filter, low tar (8-14 mg) filter, high tar (> or = 22 mg) non-filter brands and medium tar conventional filter brands (15-21 mg).

RESULTS

Irrespective of the tar level of their current brand, all current smokers had a far greater risk of lung cancer than people who had stopped smoking or had never smoked. Compared with smokers of medium tar (15-21 mg) filter cigarettes, risk was higher among men and women who smoked high tar (> or = 22 mg) non-filter brands (hazard ratio 1.44, 95% confidence interval 1.20 to 1.73, and 1.64, 1.26 to 2.15, respectively). There was no difference in risk among men who smoked brands rated as very low tar (1.17, 0.95 to 1.45) or low tar (1.02, 0.90 to 1.16) compared with those who smoked medium tar brands. The same was seen for women (0.98, 0.80 to 1.21, and 0.95, 0.82 to 1.11, respectively).

CONCLUSION

The increase in lung cancer risk is similar in people who smoke medium tar cigarettes (15-21 mg), low tar cigarettes (8-14 mg), or very low tar cigarettes (< or = 7 mg). Men and women who smoke non-filtered cigarettes with tar ratings > or = 22 mg have an even higher risk of lung cancer.

Projection of lung cancer mortality in Japan

According to the National Vital Statistics data, age-standardized mortality rates (ASRs) of lung cancer have shown slightly declining trends in Japan for both men and women. In order to evaluate whether this tendency will continue, a Bayesian age-period-cohort (APC) model was applied using the National Vital Statistics data from 1952 to 2001. In the projection, a Gaussian autoregressive prior model was applied to smooth age, period, and cohort effects from its 2 immediate predecessors by extrapolation. Posterior distributions from which we drew inferences on mortality rates were derived from 15,000 iterations using 5000 burn-in iterations. We defined the median of the iterated values as the overall summary mortality rate of the iterated results. Our results suggest that the number of deaths due to lung cancer will double for men and women during the next 3 decades due to the aging of the baby-boomer generation (individuals who were born between 1947 and 1951). Currently declining trends in some age groups will reverse and start to increase again in the next decades. However, for recent birth cohorts, the results of the projection varied according to whether the data set included early age group mortality or not. Lung cancer mortality in the future depends on the risk factors engaged in by today's young people, especially smoking. Strong promotion of anti-smoking measures and careful surveillance for lung cancer are needed.

Epidemiology of smoking-induced cardiovascular disease

Cigarette smoking is a major cause of coronary heart disease, stroke, aortic aneurysm, and peripheral vascular disease. The risk is manifest both as an increased risk for thrombosis of narrowed vessels and as an increased degree of atherosclerosis in those vessels. The cardiovascular risks owing to cigarette smoking increase with the amount smoked and with the duration of smoking. Risks are not reduced by smoking cigarettes with lower machine-measured yields of tar and nicotine, but those who have only smoked pipes or cigars seem to have a lower risk for cardiovascular diseases. Cessation of cigarette smoking reduces disease risks, although risks may remain elevated for a decade or more after cessation.

Health impact of "reduced yield" cigarettes: a critical assessment of the epidemiological evidence

Cigarettes with lower machine measured "tar" and nicotine yields have been marketed as "safer" than high tar products over the last four decades, but there is conflicting evidence about the impact of these products on the disease burden caused by smoking. This paper critically examines the epidemiological evidence relevant to the health consequences of "reduced yield" cigarettes. Some epidemiological studies have found attenuated risk of lung cancer but not other diseases, among people who smoke "reduced yield" cigarettes compared to smokers of unfiltered, high yield products. These studies probably overestimate the magnitude of any association with lung cancer by over adjusting for the number of cigarettes smoked per day (one aspect of compensatory smoking), and by not fully considering other differences between smokers of "high yield" and "low yield" cigarettes. Selected cohort studies in the USA and UK show that lung cancer risk continued to increase among older smokers from the 1950s to the 1980s, despite the widespread adoption of lower yield cigarettes. The change to filter tip products did not prevent a progressive increase in lung cancer risk among male smokers who began smoking during and after the second world war compared to the first world war era smokers. National trends in vital statistics data show declining lung cancer death rates in young adults, especially males, in many countries, but the extent to which this is attributable to "reduced yield" cigarettes remains unclear. No studies have adequately assessed whether health claims used to market "reduced yield" cigarettes delay cessation among smokers who might otherwise quit, or increase initiation among non-smokers. There is no convincing evidence that past changes in cigarette design have resulted in an important health benefit to either smokers or the whole population. Tobacco control policies should not allow changes in cigarette design to subvert or distract from interventions proven to reduce the prevalence, intensity, and duration of smoking.

Indoor burning coal air pollution and lung cancer--a case-control study in Fuzhou, China

A case-control study on risk factors for lung cancer was carried out in Fuzhou, China. One-hundred and two newly-diagnosed primary lung cancer cases in urban Fuzhou (78 male and 24 female cases) were matched with 306 population-based controls. The primary histological types were adenocarcinomas (57 cases, 55.9%) and squamous cell carcinomas (39 cases, 38.2%). Controls were obtained from the general population by random, stratified sampling and consisted of noncancer cases matched for sex, ethnicity and age. Cases and controls were interviewed by trained professionals using a standardized questionnaire. Information was obtained on: smoking habits, living conditions, history of respiratory diseases, air pollution, and 40 other variables. The data were evaluated by conditional logistic regression analysis. The major risk factors for lung adenocarcinoma were: indoor air pollution from burning coal, chronic bronchitis, and high economic income. The risk factors for lung squamous cell carcinoma were: amount of cigarettes smoked per day, "deep inhalation", a history of exposure to environmental tobacco smoke (ETS) before 20 years of age, burning coal indoors, and high economic income. The results showed that the major risk factors for lung cancer in Fuzhou were: burning coal indoors, smoking, exposure to ETS before 20 years of age, chronic bronchitis, and high economic income. Cigarette smoking significantly increased the risk of lung squamous cell carcinoma, but had no significant association with the risk of lung adenocarcinoma. In summary, our research supports the hypothesis that smoking and indoor air pollution are the major risk factors for lung cancer in Fuzhou. Burning coal indoors and smoking were associated with lung cancer mortality in a major city in southern China.

The epidemiology of lung cancer in women

Female lung cancer mortality rates have increased dramatically since 1950, and in 1987 lung cancer surpassed breast cancer as the leading cause of cancer death among US women. The epidemic in women, as in men, is attributable to cigarette smoking. Smoking prevalence in women peaked in the 1960s and 1970s and has since been declining, although fully 23.5% of adult women were current smokers in 1991. As a reflection of declines in smoking prevalence, lung cancer incidence and mortality rates are declining slightly in women under 45 years old, and it is predicted that overall age-adjusted rates may begin to turn around early in the next century. Survival for the disease is poor; the relative 5-year survival rate for women diagnosed between 1981 and 1987 was only 16% for whites and 13% for African-Americans. This article describes trends in female lung cancer rates by race and age, provides staging and survival statistics, and briefly reviews the evidence on smoking and other risk factors (environmental tobacco smoke, radon, pollution, family history, previous lung disease, and diet) for lung cancer in women.

Changes in patterns of cigarette smoking and lung cancer risk: results of a case-control study

Data from a case-control study on lung cancer were used to evaluate how changes in cigarette habits, mainly smoking cessation, switch from non-filter to filter brands, from dark to light tobacco, or from handrolled to manufactured cigarettes, and reduction in daily consumption influence lung cancer risk. The results presented concern all males, exclusive cigarette smokers, involved in the study, i.e. 1,057 histologically confirmed lung cancer and 1,503 matched controls. The general decrease in lung cancer risk with the years since cessation was also found in each subgroup of cigarette exposure defined by duration of smoking, daily consumption and type of cigarettes smoked. Among smokers who had given up smoking from less than 10 years earlier, the lung cancer risks were two-fold higher for those who had stopped smoking for coughing or health reasons than for those who had stopped smoking for reasons other than health problems. A decrease in lung cancer risk, although not significant, was found in people who switched from non-filter brands to filter brands and from dark to light tobacco and in smokers who reduced their daily consumption of cigarettes by more than 25% as compared to smokers who had not changed habits.

Smoking and passive smoking in relation to lung cancer in women

In a population based case-control study the association between female lung cancer and some possible etiological agents was investigated; 210 incident cases in Stockholm county, Sweden, and 209 age-matched population controls were interviewed about their exposure experiences according to a structured questionnaire. A strong association between smoking habits and lung cancer risk was found for all histological subgroups. Relative risks for those who had smoked daily during at least one year ranged between 3.1 for adenocarcinoma to 33.7 for small cell carcinoma in a comparison with never-smokers. All histological types showed strong dose-response relationships for average daily cigarette consumption, duration of smoking, and cumulative smoking. There was no consistent effect of parental smoking on the lung cancer risk in smokers. Only 38 cases had never been regular smokers and the risk estimates for exposure to environmental tobacco smoke were inconclusive. The high relative risks of small cell and squamous cell carcinoma associated with smoking may have implications for risk assessments regarding passive smoking.