Lung cancer risk and cigarette smoking, lung tuberculosis according to histologic type and gender in a population based case–control study
Introduction
Lung cancer is the most common cancer in the world since 1985. The annual number of new cases was estimated to be 12.4% of all new cancer cases, and accounts for 29% of all cancer deaths [1]. Lung cancer mortality among Koreans has increased tremendously; the mortality rate has risen from 2.1 to 33 (per 100,000) among men and from 1.3 to 13.5 (per 100,000) among women from 1980 to 2000 [2].
Cigarette smoking is a major risk factor in the etiology of lung cancer [3]. The strength of the association varies with histologic type; the association is stronger for squamous cell carcinoma (SqCC) and small cell carcinoma (SmCC) than large cell cancer, and adenocarcinoma (ADCC) has a relatively weaker association [4].
In Korea, although smoking has decreased in both gender groups, the high smoking rate among men is in contrast to the low rate among women (68.3% in 1990, 52.2% in 2006 among males; 6.0% in 1990, 3.9% in 2006 among females) [5]. Cigarette smoking is the most important risk factor but smoking alone does not explain the incidence of lung cancer among women who have never smoked. Among possible risk factors, we examined pulmonary tuberculosis because presence of tuberculosis for numerous years may increase a person's chance of developing lung cancer in areas of the lung that are scarred from lung tuberculosis [6]. Since lung tuberculosis is still prevalent in Korea (2.54 per 1000) [7], lung tuberculosis is a possible risk factor for lung cancer.
Additionally, several epidemiologic studies reported that women are more susceptible to the carcinogenic effects of cigarette smoke given comparable amounts of cigarette smoke exposure [8], [9]. In particular, ADCC was reported to be more prevalent among females than males [10], [11], [12], [13]. However other studies [14], [15] presented no difference in risk, thereby generating substantial controversy.
In this study, we examined whether the strength of the association of cigarette smoking differs according to major histological type and gender, and assessed other risk factors, in particular tuberculosis, that are associated with lung cancer risk.
Section snippets
Study population
Cases were recruited from the Korean Academy of Tuberculosis and Respiratory Diseases (KATRD), a nationwide hospital-based lung cancer study conducted in 1998 where histologically confirmed incident lung cancer cases (n = 4210) diagnosed in 1997 were registered in the database. Of these cases, after excluding patients with metastatic lung cancer from other primary sites, clinically diagnosed cases without pathologic verification (n = 118), and overlapping cases diagnosed at more than one hospital (n
Results
Table 1 details the basic characteristics of the eligible population and the study population after age and sex matching. Age, sex, past and current history of lung tuberculosis, family history of lung cancer, and occupational history of high risk job were all significantly different between cases and controls in the eligible population. In the study population, only sex and past and current history of lung tuberculosis remained significantly different.
Table 2 shows the OR (95% CI) for the
Discussion
Our findings present a significant dose–response relationship of cigarette smoking and risk of lung cancer for the three major histologic types, although the association was weaker for ADCC. The strength of the association was more pronounced in females than males. Among males, history of tuberculosis was associated with SqCC and ADCC but not SmCC. While the additive combined effect between tuberculosis and smoking varied according to histologic type, smokers with tuberculosis had a
Conflict of interest statement
The authors declare no conflict of interest.
Acknowledgements
This work was supported by the Korea Research Foundation Grant (grant number: KRF-2002-002-E00031). We appreciate the active participation of all members of the Korean Academy of Tuberculosis and Respiratory Disease.
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