香港女性肺癌,空气污染抑或饮食？：饮食,空气污染与肺癌关系的混杂因素

从世界范围来说，住在香港、夏威夷、旧金山和新加坡的华裔妇女肺癌发病率相对较高，然而吸烟率低。过去１５年我们以室内空气污染（ＥＴＳ，烧香，烹调污染）为重点，并以饮食为可能因素来探讨它们与肺癌的关系，但未发现这些空气污染物与肺癌有联系。吸烟者（吸烟量已作了调整）即使有４０年以上烧香史，肺癌危险性仍下降了８３％（趋势检验Ｐ＝０．０１）。不吸烟妇女（年龄、生育史、文化程度已调整）从事烹调即使超过４０年，肺癌危险性仍下降６３％（Ｐ＝０．００１）。可见结果与预期相反，但可用饮食因素来解释。吸烟者中烧香的妇女往往比不烧香的妇女喜欢吃“健康饮食”；不吸烟者参与烹调多年的妇女也更喜欢吃“健康饮食”。健康饮食是指较多吃鲜鱼、蔬菜、水果和较少吃经防腐处理过的食品、辣酱和饮酒，前类食物使香港华人妇女肺癌危险性降低，后者则使之增高，可见饮食因素起着混杂因子的作用，使评价空气污染对肺癌危险性的影响蒙上阴影     

Women and lung cancer: does oestrogen play a role?

Smoking-related disease remains a major public-health problem. Large numbers of women continue to smoke, and new smokers are almost as likely to be female as male. Lung cancer is still a largely incurable disease; annual lung-cancer mortality in women exceeds that of breast cancer, and lung cancer now accounts for 12% of all new female cancer cases. The results of several studies suggest that women are more susceptible than men to lung cancer and to conditions that predispose to this cancer, such as chronic obstructive pulmonary disease. There is still much controversy about whether there is an increased lung-cancer risk in women across all populations. Many epidemiological studies have been negative or equivocal when comparing male and female lung-cancer risk. This article is not intended to be a comprehensive review of all epidemiological studies, or of all possible lung-cancer risk factors. Lung-cancer incidence and risk in women are discussed, and evidence for possible mechanisms of increased female risk are presented, including the role of oestrogen in the development of lung cancer.     

美国吸烟者与非吸烟者肺癌流行病学概况

人们已清楚知道，吸烟是肺癌的主要危险因素，也知道吸烟和职业暴露以外的因素在某些肺癌特别是腺癌中起作用。本文以医院病例为基础进行大样本的病冽对照研究来分析肺癌与吸烟因素（吸烟量，过滤咀烟，黑白人种的吸烟习惯）及非吸烟因素（ＥＴＳ暴露，原发性肿瘤和治疗，生殖和内分泌因素，躯体指数）的联系。虽然吸烟与所有主要细胞类型的肺癌都有剂量－效应关系，但与腺癌的联系强度较弱，提示吸烟以外的因素对腺癌的重要性。在白人和黑人中，无论男、女，肺癌的ＯＲ值均随香烟焦油摄入量的增加而增加，并随戒烟年限的延长而减少。是否吸含薄荷香烟，对肺癌的危险性影响不大。未见到ＥＴＳ与肺癌的联系，即使丈夫吸烟也未能使不吸烟妻子患肺癌的危险性增加。生殖系统原发性肿瘤和放射治疗，可使不吸烟女性患肺癌的危险性增加４倍。曾观察到身体瘦弱与现在吸烟、以前吸烟和从不吸烟的女性肺癌之间的联系。以上结果在本文中分别加以讨论。总的来说，人群中肺癌患病率的不同，可能由于：（１）香烟烟雾中的致癌物不同；（２）香烟烟雾的作用因素不同，包括受到机体敏感性及对致癌物的代谢的影响；（３）暴露于吸烟以外的其他各种危险因素     

Reproductive and hormonal factors and risk of lung cancer in women: a prospective cohort study

Several lines of evidence suggest that endocrine factors may play a role in the development of lung cancer, but the evidence is limited and inconsistent. We investigated the association of reproductive and hormonal factors with risk of lung cancer in the National Breast Screening Study, which included 89,835 Canadian women aged 40-59 years at recruitment between 1980 and 1985. Linkages to national cancer and mortality databases provided data on cancer incidence and deaths from all causes, respectively, with follow-up ending between 1998 and 2000. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (95% CI) for the association between hormonal factors and lung cancer. During a mean of 16.4 years of follow-up, we observed 750 incident lung cancer cases. After adjustment for covariates, parous women were not at increased risk of lung cancer (HR = 1.18, 95% CI 0.94-1.47) relative to nulliparous women; however, there was a modest increase in risk with increasing parity, reaching a HR of 1.42, 95% CI 1.06-1.88 in women who had 5 or more live births (p for trend 0.02). Among parous women, age at first live birth was inversely associated with risk. Women who had their first live birth at age 30 or older were at reduced risk relative to women who had their first live birth below age 23 (HR 0.68, 95% CI 0.50-0.93, p for trend 0.004). These associations did not differ by age at enrollment (40-49 vs. 50-59 years old), but were somewhat strengthened when attention was restricted to never smokers. Ever use of exogenous hormones showed little association with lung cancer risk; however, long-term users of hormone replacement therapy were at slightly increased risk. Our results add to the limited existing evidence that certain reproductive and hormonal factors may be associated with lung cancer risk in women.     

An epidemiological study on occupation and cancer risk

The relation between occupation and cancer risk was examined on the basis of 17,164 male and 6,835 female cancer patients aged 30 years or over who were entered in the Aichi Cancer Registry during the period, 1979-1987. Controlling for age, the risk of developing lung cancer was significantly high in sales, transport-and-communications, mental, ceramics and construction workers in men, and service workers in women. The risk of developing liver cancer was significantly high in transport-and-communications and service workers in men. The risk of developing colon cancer was significantly high in professional people of both sexes and in clerical workers in men. The risk of developing female breast cancer was significantly high in professional women, administrative and clerical workers and hairdressers. The risk of developing stomach cancer was significantly high in male and female agricultural workers, while that of developing cancer of the mouth-and-pharynx was significantly high in construction workers in men and filature-and-spinning workers in women. Analysis of smoking and alcohol drinking habits, by occupation, suggested the increased risk of developing lung cancer to be associated with a greater percentage of smokers and the increased risks of developing cancers of the liver and mouth-and-pharynx to be associated with a greater percentage of daily alcohol drinkers. When the analysis was limited to smokers, the risk of developing lung cancer was still significantly high in metal, ceramics and construction workers in men.     

Risk factors for lung cancer in Iowa women: implications for prevention

BACKGROUND: Multiple risk factors possibly associated with lung cancer were examined as part of a large-scale residential radon case-control study conducted in Iowa between 1994 and 1997. We were particularly interested in stratifying risk factors by smoking status. Relatively little risk factor information is available for Midwestern rural women. METHODS: Four hundred thirteen female lung cancer cases and 614 controls aged 40-84, who were residents of their current home for at least 20 years, were included. Risk factors examined included cigarette smoking, passive smoking, occupation, chemical exposure, previous lung disease, family history of cancer, and urban residence. Multiple logistic regression analysis was conducted after adjusting for age, education, and cumulative radon exposure. RESULTS: As expected, active cigarette smoking was the major risk factor for lung cancer. While cessation of smoking was significantly associated with a reduced risk for lung cancer, the risk remained significantly elevated for 25 years. Among all cases, asbestos exposure was a significant risk. Among ex-smokers, pack-year history predominated as the major risk. Among never smokers, a family history of kidney or bladder cancer were significant risk factors (OR=7.34, 95% CI=1.91-28.18; and OR=5.02, 95% CI=1.64-15.39, respectively), as was a history of previous lung disease (OR=2.28, 95% CI=1.24-4.18) and asbestos exposure. No statistically significant increase in lung cancer risk was found for occupation or urban residence. CONCLUSIONS: Smoking prevention activities are urgently needed in rural areas of the United States. Relatives of individuals with smoking-related cancers are potentially at increased risk. Genetic risk factors should be more fully investigated in never smokers.     

Gender- and smoking-related bladder cancer risk

BACKGROUND: There is growing evidence that, when smoking habits are comparable, women incur a higher risk of lung cancer than men. Because smokers are also at risk for bladder cancer, we investigated possible sex differences in the susceptibility to bladder cancer among smokers. METHODS: A population-based, case--control study was conducted in Los Angeles, CA, involving 1514 case patients with bladder cancer and 1514 individually matched population control subjects. Information on tobacco use was collected through in-person interviews. Peripheral blood was collected from study participants to measure 3- and 4-aminobiphenyl (ABP)-hemoglobin adducts, a marker of arylamine exposure. Data were analyzed to determine whether the risk of bladder cancer differs between male and female smokers and whether female smokers exhibit higher levels of ABP-hemoglobin adducts than male smokers with comparable smoking habits. All statistical tests were two-sided. RESULTS: Cigarette smokers had a statistically significant 2.5-fold higher risk (95% confidence interval = 2.1 to 3.0) of bladder cancer than never smokers. Use of filtered versus nonfiltered cigarettes, low-tar versus higher tar cigarettes, or the pattern of inhalation did not modify the risk. The risk of bladder cancer in women who smoked was statistically significantly higher than that in men who smoked comparable numbers of cigarettes (P =.016 for sex-lifetime smoking interaction). Consistent with the sex difference in smoking-related bladder cancer risk, the slopes of the linear regression lines of the 3- and 4-ABP--hemoglobin adducts by cigarettes per day were statistically significantly steeper in women than in men (P values for sex differences <.001 and.006, respectively). CONCLUSION: The risk of bladder cancer may be higher in women than in men who smoked comparable amounts of cigarettes.     

The association of physical activity with lung cancer incidence in a cohort of older women: the Iowa Women's Health Study.

BACKGROUND: We examined the potential association between physical activity and lung cancer in women. METHODS: In 1986, 36,929 women from Iowa, who were free of prior cancer, completed a questionnaire regarding physical activity, smoking, body mass index, and other life-style factors. Women were followed through 2002 for cancer incidence. RESULTS: After adjusting for potential confounders, women with high physical activity levels were less likely [hazard ratio, 0.77; 95% confidence intervals (CI), 0.64-0.94] to develop lung cancer than women with low activity levels. This hazard ratio was 0.72 (95% CI, 0.55-0.94) in current smokers and 0.63 (95% CI, 0.43-0.92) in former smokers, but was not significant in never smokers. CONCLUSION: These results suggest that physical activity might reduce the risk of lung cancer in women who are current or former smokers.     

Lung cancer screening in high-risk populations

Although the number of smokers per capita has declined appreciably in the United States in the past 30 years, smokers still make up about one quarter of the adult population. It does not appear that the number of US smokers will decrease further in the next century, and the number may even increase due to the popularity of smoking among teenagers. Epidemiological data indicate that women are more susceptible, dose-for-dose, to the adverse effects of tobacco smoke. Since women make up a large percentage of today s smokers, lung cancer rates may increase in the future. Current guidelines recommend against lung cancer screening based on chest x-ray and sputum morphology; however, new highly sensitive detection methods are available that may make screening more effective, especially if combined with analysis of risk factors for lung cancer and biomarkers of damage to the airways that may identify individuals at highest risk for lung malignancies. Lung cancer will continue to be a major public health problem in the next century. Advances in the field of early detection may make lung cancer screening practical and effective in the near future.     

Lung cancer risk reduction after smoking cessation: observations from a prospective cohort of women.

PURPOSE: We conducted this study because the duration of excess lung cancer risk among former smokers has been inconsistently reported, doubt has been raised regarding the population impact of smoking cessation, and differential risk reduction by histologic cell type after smoking cessation needs to be confirmed. METHODS: The Iowa Women's Health Study is a prospective cohort study of 41,836 Iowa women aged 55 to 69 years. In 1986, mailed questionnaires were used to collect detailed smoking history. Age-adjusted lung cancer incidence through 1999 was analyzed according to years of smoking abstinence. Relative risks were estimated using Cox regression analysis. RESULTS: There were 37,078 women in the analytic cohort. Compared with the never smokers, former smokers had an elevated lung cancer risk (relative risk, 6.6; 95% confidence interval, 5.0 to 8.7) up to 30 years after smoking cessation for all former smokers. However, a beneficial effect of smoking cessation was observed among recent and distant former smokers. The risk of adenocarcinoma remained elevated up to 30 years for both former heavier and former lighter smokers. CONCLUSION: The risk for lung cancer is increased for both current and former smokers compared with never smokers and declines for former smokers with increasing duration of abstinence. The decline in excess lung cancer risk among former smokers is prolonged compared with other studies, especially for adenocarcinoma and for heavy smokers, suggesting that more emphasis should be placed on smoking prevention and lung cancer chemoprevention.     

Risk factors for primary lung cancer among never smokers by gender in a matched case–control study

Objective

Lung cancers that occur in never smokers differ from those that occur in smokers. We performed an analysis of potential epidemiological risk factors for lung cancer among never smokers.

Methods

In this hospital-based matched case–control study, all 1,540 matched case–control pairs were Han Chinese in Taiwan. The data on demographic characteristics, smoking habit, exposure to environmental tobacco smoke, medical history of lung diseases, family history of lung cancer, and female characteristics were collected from a structured questionnaire. A multiple conditional logistic regression was used to estimate odds ratios and 95 % confidence intervals after adjusting for possible confounders.

Results

Overall, several epidemiological factors of lung cancer in never smokers were different between males and females. For the female population, subjects who were exposed to environmental tobacco smoke (OR = 1.39, 95 % CI = 1.17–1.67) with a history of pulmonary tuberculosis and with family history of lung cancer in first-degree relatives (OR = 2.44, 95 % CI = 1.79–3.32) had higher risk of lung cancer, while subjects with a history of hormone replacement therapy and using fume extractors for those who cooked were protective. For the male population, only subjects with family history of lung cancer in first-degree relatives (OR = 2.77, 95 % CI = 1.53–5.01) were significantly associated with risk of lung cancer.

Conclusion

This study provides insights about the epidemiological factors of lung cancer in never smokers, adding to existing evidence that family history of lung cancer and environmental tobacco smoke may moderate lung cancer risk.     

Molecular epidemiology to better predict lung cancer risk

Although it is clear that smoking causes lung cancer, it is not known why some smokers develop the disease while others do not. Little is also known regarding risk factors for lung cancer among never-smokers, particularly women, or why women with lung cancer are more likely to have a family history of cancer, to be diagnosed at a young age, or to have adenocarcinoma. The application of molecular epidemiology to the study of lung cancer risk might facilitate elucidation of these questions. In this review, the molecular epidemiology of lung cancer is discussed, with an emphasis on studies of genetic variability in metabolic pathways as a means for determining susceptibility. Work that has assessed intermediate markers of risk, such as DNA adducts, is also presented, as are studies of tumor tissue alterations, such as mutations and DNA methylation, in relation to risk of lung cancer. Finally, approaches to evaluating factors that might explain the differing epidemiology of lung cancer between men and women are also presented. It is likely that, by incorporating biomarkers of susceptibility, exposure, and effect, molecular epidemiologic approaches might better define factors that explain some of the variability in lung cancer risk.     

Diet, reproductive factors and lung cancer risk among Chinese women in Singapore: evidence for a protective effect of soy in nonsmokers.

The factors associated with risk of lung cancer among nonsmokers have not been fully elucidated, but dietary factors have consistently been shown to play a role. Chinese women are unique in having a high incidence of lung cancer despite a low smoking prevalence. This population is also known to have a high intake of soy, a dietary source of phytoestrogens. We conducted a hospital-based case-control study among Singapore Chinese women, comprising 303 cases and 765 age-matched controls, of whom 176 cases and 663 controls were lifetime nonsmokers. Data on demographic background, reproductive factors and dietary intake of fruit, vegetables and soy foods were obtained by in-person interview. We observed an inverse association between intake of total, cruciferous and non-cruciferous vegetables and risk of lung cancer among smokers. Although smokers in the highest tertile of fruit intake also had a lower risk, this was not statistically significant. Higher intake of soy foods significantly reduced risk of lung cancer among lifetime nonsmokers, but not among smokers. When soy isoflavonoid intake in mg/week was computed based on frequency and portion size of intake of eight common local soy foods, the adjusted OR among nonsmokers for the highest tertile compared to the lowest was 0.56, 95% CI 0.37-0.85 (p for trend <0.01). Fruit intake was also significantly associated with reduced lung cancer risk among nonsmokers, but the effect was not significant after adjustment for soy intake. On the other hand, soy intake remained an independent predictor of risk after controlling for fruit intake. Reproductive effects were also primarily confined to lifetime nonsmokers, among whom having 3 or more livebirths (adjusted OR 0.65, 0.44-0.96) and a menstrual cycle length of more than 30 days (OR 0.46, 0.25-0.84) accorded a significantly reduced risk of lung cancer. Place of birth was significantly associated with risk among nonsmokers (OR 2.6, 1.7-3.9 for China-born vs. local born) but not among smokers. When analysis was restricted to nonsmokers with adenocarcinomas, the dietary effects were consistent or enhanced. On stepwise regression, soy intake and cycle length emerged as the independent dietary and reproductive predictors of lung cancer risk in nonsmokers. These findings are consistent with other evidence suggesting an involvement of estrogen-related pathways in lung cancer among non-smoking women.     

中青年与老年非吸烟女性肺癌危险因素的比较研究

目的 分析比较中青年和老年非吸烟女性肺癌的危险因素。方法 于1992年2月～1993年12月，在上海市区完成了一项大规模全人群女性肺癌病例对照研究，共调查了非吸烟女性肺癌病例504例及人群对照601例。根据年龄把研究对象分为两组，35～54岁和55～69岁组，并分析比较两组的结果。单因素分析采用Mantel—Haenszel分层分析法，进一步调整混杂因素采用多变量logistic回归模型。结果分析结果显示，中青年组危险因素是做饭时眼和喉烟雾刺激感，最高一组比数比为3．40；其次是肺癌家族史，比数为5．80。而保护因素是饮茶(OR：0．40)和活产次数(5次及以上组OR：0．39)。老年组的危险因素主要是：高身体指数(最高一组OR：1．69)、工作场所被动吸烟史(OR：1.55)、厨房在卧室内(OR：1．50)、做饭时厨房内烟雾较多(OR：2．43)、菜油为主要食用油(OR：1.94)等。此外。肺结核病史和肺癌家族史可能增加老年女性患肺癌的危险性。保护因素是维生素C(最高一组OR：0．45)，趋势检验有统计学意义。中青年组和老年组肺癌的结果比较表明，无论是危险因素还是保护因素，两者都有不同。结论 中青年和老年非吸烟女性肺癌的病因可能存在一定的差异。     

Cruciferous vegetables consumption and the risk of female lung cancer: a prospective study and a meta-analysis

BackgroundEpidemiological studies evaluating the association between cruciferous vegetables (CVs) intake and female lung cancer risk have produced inconsistent results.Patients and methodsThis study followed 74 914 Chinese women aged 40–70 years who participated in the Shanghai Women's Health Study. CV intake was assessed through a validated food-frequency questionnaire (FFQ) at baseline and reassessed during follow-up. Hazard ratios (HRs) and 95% confidence interval (CIs) were estimated by using Cox proportional hazards models. Furthermore, we carried out a meta-analysis of all observational studies until December 2011.ResultsAfter excluding the first 2 years of follow-up, 417 women developed lung cancer over a mean of 11.1 years of follow-up. An inverse association of borderline statistical significance was observed between CV consumption and female lung cancer risk, with HR for the highest compared with the lowest quartiles of 0.73 (95% CI 0.54–1.00, P trend = 0.1607). The association was strengthened in analyses restricting to never smokers, with the corresponding HR of 0.59 (95% CI 0.40–0.87, P trend = 0.0510). The finding of an inverse association between CV intake and lung cancer risk in women was supported by our meta-analysis of 10 included studies.ConclusionsOur study suggests that CV consumption may reduce the risk of lung cancer in women, particularly among never smokers.     

Environmental tobacco smoke and lung cancer mortality in the American Cancer Society's Cancer Prevention Study II

Environmental tobacco smoke (ETS) has been classified as a human lung carcinogen by the United States Environmental Protection Agency (EPA), based both on the chemical similarity of sidestream and mainstream smoke and on slightly higher lung cancer risk in never-smokers whose spouses smoke compared with those married to nonsmokers. We evaluated the relation between ETS and lung cancer prospectively in the US, among 114,286 female and 19,549 male never-smokers, married to smokers, compared with about 77,000 female and 77,000 male never-smokers whose spouses did not smoke. Multivariate analyses, based on 247 lung cancer deaths, controlled for age, race, diet, and occupation. Dose-response analyses were restricted to 92,222 women whose husbands provided complete information on cigarette smoking and date of marriage. Lung cancer death rates, adjusted for other factors, were 20 percent higher among women whose husbands ever smoked during the current marriage than among those married to never-smokers (relative risk [RR]=1.2, 95 percent confidence interval [CI]=0.8-1.6). For never-smoking men whose wives smoked, the RR was 1.1 (CI=0.6-1.8). Risk among women was similar or higher when the husband continued to smoke (RR=1.2, CI=0.8-1.8), or smoked 40 or more cigarettes per day (RR=1.9, CI=1.0-3.6), but did not increase with years of marriage to a smoker. Most CIs included the null. Although generally not statistically significant, these results agree with the EPA summary estimate that spousal smoking increases lung cancer risk by about 20 percent in never-smoking women. Even large prospective studies have limited statistical power to measure precisely the risk from ETS.     

Prior Lung Disease and Risk of Lung Cancer in a Large Prospective Study

OBJECTIVES: While 75-90% of people who develop lung cancer are smokers, only a small proportion of smokers develop lung cancer. Identifying factors that increase a smoker's risk of developing lung cancer may help scientists to better understand the etiology of lung cancer and more effectively target high-risk groups for screening. METHODS: Information on physician-diagnosed non-malignant lung diseases [asbestosis, asthma, chronic bronchitis or emphysema (CB/E), pneumonia, and tuberculosis] was obtained at baseline from 17,698 men and women involved in CARET, a randomized lung cancer prevention trial of beta-carotene and vitamin A among heavy smokers and asbestos-exposed workers. Hazard ratios for lung cancer were estimated through Cox regression models, after controlling for potential confounding factors, included smoking. Analyses were restricted to former and current smokers. RESULTS: During a median follow up of 9.1 years, 1028 cases of lung cancer occurred. Those who developed lung cancer were more likely to report a history of CB/E than controls (adjusted HR = 1.29, 95% CI: 1.09-1.53). In subgroup analyses, the association between a history of CB/E and lung cancer was stronger for those who were younger at diagnosis/reference, men in the heavy smoker cohort, former smokers, and those with squamous cell carcinomas. There was little association between a history of other lung diseases and lung cancer. CONCLUSIONS: Smokers with a history of CB/E may be at higher risk of developing lung cancer, independent of their smoking history.     

Risk factors for oesophageal,lung, oral and laryngeal cancers in black South Africans

The authors used data collected from 1995 to 1999, from an on-going cancer case-control study in greater Johannesburg, to estimate the importance of tobacco and alcohol consumption and other suspected risk factors with respect to cancer of the oesophagus (267 men and 138 women), lung (105 men and 41 women), oral cavity (87 men and 37 women), and larynx (51 men). Cancers not associated with tobacco or alcohol consumption were used as controls (804 men and 1370 women). Tobacco smoking was found to be the major risk factor for all of these cancers with odds ratios ranging from 2.6 (95% CI 1.5-4.5) for oesophageal cancer in female ex-smokers to 50.9 (95% CI 12.6-204.6) for lung cancer in women, and 23.9 (95% CI 9.5-60.3) for lung cancer and 23.6 (95% CI 4.6-121.2) for laryngeal cancer in men who smoked 15 or more grams of tobacco a day. This is the first time an association between smoking and oral and laryngeal cancers has been shown in sub-Saharan Africa. Long-term residence in the Transkei region in the southeast of the country continues to be a risk factor for oesophageal cancer, especially in women (odds ratio=14.7, 95% CI 4.7-46.0), possibly due to nutritional factors. There was a slight increase in lung cancer (odds ratio=2.9, 95% CI 1.1-7.5) in men working in 'potentially noxious' industries. 'Frequent' alcohol consumption, on its own, caused a marginally elevated risk for oesophageal cancer (odds ratio=1.7, 95% CI 1.0-2.9, for women and odds ratio=1.8, 95% CI 1.2-2.8, for men). The risks for oesophageal cancer in relation to alcohol consumption increased significantly in male and female smokers (odds ratio=4.7, 95% CI=2.8-7.9 in males and odds ratio=4.8, 95% CI 3.2-6.1 in females). The above results are broadly in line with international findings.     

Gender susceptibility for cigarette smoking-attributable lung cancer: A systematic review and meta-analysis

Objectives

As the primary cause of lung cancer, whether smoking confers the same risk of lung cancer for women as men is unclear. Therefore, we aimed to compare male and female susceptibility for cigarette smoking-attributable lung cancer.

Methods

A systematic review and meta-analysis was conducted by searching articles published up to July 2013 in three online databases (MEDLINE, EMBASE, and Cochrane Database). All studies estimated the association of cigarette smoking with the risk of lung cancer between men and women, respectively. A random effects model with inverse variance weighting was used to pool data. Male to female ratio of relative risk (RRR) was calculated to compare male and female susceptibility for cigarette smoking-attributable lung cancer.

Results

47 articles containing 404,874 individuals were included in the final analysis. Compared with non-smokers, male to female RRR was 1.61 (95%CI: 1.37, 1.89) among current smokers. Based on pathological type, adenocarcinoma had the highest RRR (1.42; 95%CI: 0.86, 2.35), followed by squamous cancer and small cell lung cancer. Furthermore, compared with non-smoking men, current smoking men had higher risk of lung cancer than women in spite of smoking quantity, smoking duration or years since quitting.

Conclusions

These findings indicated that males had higher susceptibility for cigarette smoking-attributable lung cancer than females. It is contradicted with traditional opinion that females would be more easily suffered from cigarette smoking-attributable health problems than males. Hence, tobacco control is very crucial in both males and females.     

Time trends of lung cancer incidence by histologic types and smoking prevalence in Hong Kong 1983-2000

The gender difference in epidemiology of lung cancer has been postulated to be due to the higher susceptibility of women to risk factors especially tobacco smoking. Alternatively, such difference may also be explained by some unknown gender-specific etiological factors, which can have been masked if both the female and male prevalence of smoking are high. Hong Kong has a low female smoking prevalence rate and therefore the trend of the female incidence of lung cancer is particularly interesting because it can reflect the effects of the non-smoking related risk factors more clearly. The present study examined the trends of incidence rates for the major histologic types and smoking prevalence from 1983 to 2000 in Hong Kong with respect to gender. The prevalence of daily smokers decreased from 39.7% in 1982 to 22% in 2000 in males and from 5.6 to 3.5% in females. The time trends of the lung cancer incidence (overall or with respect to age and histology) were similar for both genders. The overall incidence decreased progressively throughout the study period, attributable to the decrease in squamous cell, small cell and large cell carcinoma. The decline occurred in all age groups but to a greater extent in the younger age groups. The incidence of adenocarcinoma increased until 1988-1990 and then stabilized. The initial increase was restricted to the older age groups. These temporal patterns suggested that the same etiological factors affected both genders to a different extent but manifested as similar changes in the direction of incidence over time. To confirm this hypothesis, further studies were needed to clarify the nature of these etiological factors for the non-smoking related lung cancer cases.