Epidemiology of Lung Cancer

Age and Gender

Whereas lung cancer incidence in men in the United States declined after peaking in the mid-1980s, the pattern in women differed significantly. In women, lung cancer incidence more than doubled between 1975 and 2000. Age-adjusted incidence in women increased on average by 4.1% per year between 1973 and 1990, but during 1990–2000, the average annual increase was only 0.2%. Among men and women, the rates declined during the past   10 years particularly among those under age 60, but continued to increase among those over age 70 . Only 5% to 10% of lung cancer cases are diagnosed under 50 years of age. Epidemiologic studies of lung cancer in young adults emphasize the predominance of adenocarcinomas and the importance of a positive family history. The current smoking prevalence and magnitude of estimates of relative risk due to the average intensity and duration of smoking in women in the United States appear to be converging on the patterns in similarly exposed and aged males. Among whites, the male to female age-standardized lung cancer incidence rate ratio is about 1:6, or 60% higher in males.

 Compared with women, men generally began smoking cigarettes at an earlier age, smoked more cigarettes per day and for a longer duration, inhaled more deeply, and consumed cigarettes with higher tar content. With increasing prevalence and duration of tobacco smoking in women after World War II, lung cancer mortality increased substantially in North America and Western Europe. Several recent controlled observational studies have even suggested that female smokers have a higher relative risk of lung cancer than male smokers, after adjusting for age and average daily intensity of smoking exposure. After controlling for past smoking history, other studies have suggested that women are more susceptible to chronic obstructive pulmonary disease or exhibit more rapid rates of decline in pulmonary function. In a prospective study conducted in Copenhagen, Denmark, although rate ratios for all histologic types of lung cancer increased with number of pack-years of exposure for both men and women, the relative risks did not differ between men and women, after adjusting for age and duration and intensity of smoking. A randomized chemo prevention trial was conducted by the British Columbia Cancer Agency in Vancouver among current and former smoking men and women with at least 20 pack-years of tobacco smoke exposure. The prevalence of pretrial high-grade preinvasive neoplastic bronchial epithelial changes, and of airflow obstruction (forced expiratory volume in 1 second/forced vital capacity value of 70% or less) was lower in women than in men of comparable age. The case-control design and the method of estimation of odds ratios in women may have been susceptible to recall bias, under reporting of amount smoked by the cases, and differences in baseline risk factors for lung cancer between male and female nonsmoking controls (i.e., occupational risk factors, nutritional risk factors, unmeasured exposure to environmental tobacco smoke, etc.). However, the question of gender differences in susceptibility to tobacco smoking merits further investigation. Prospective studies are required to derive unconfounded incidence measures of absolute or attributable risk that may be compared in smoking and nonsmoking men and women.

 

 

Race and Ethnicity

In the United States, the risk of lung cancer in black men has been about 50% higher than that in white men in the past 10–15 years, but the annual rate of decline after 1990 in black men (—2.5%) was about equal to that in white men (—2.3%) (Table 1.1). Among black men, lung cancer mortality was the second leading cause of death, ranking below coronary heart disease. The excess mortality from lung cancer among black men, compared with white men, was greatest for the age interval 35–64 years. Cohorts of white men born before 1900 had higher (50%) age-specific rates than black men; but this pattern reversed after 1915.

 In the United States, during 1975–1990, the age-adjusted lung cancer incidence in black women was 10% to 20% higher than that in white women; during the past 10 years the average annual rate in black women (39.3 per 100,000) was slightly less than that in white women (40.9 per 100,000). After 1990, the incidence rates have continued to increase at an average annual rate of 0.7%–0.8% for black and white women.

 

 

Socioeconomic Status

Various studies have reported an inverse association between lung cancer mortality and socioeconomic status. A two-fold gradient in mortality was observed between low and high social class, as measured by occupation, income, or education. Smoking patterns accounted for part of the differential risk by social class, with smoking prevalence rates increased among blue-collar workers and among those with lower levels of education. Socioeconomic status may also serve as a surrogate measure for other risk factors such as occupation, diet, and ambient air pollutants, and may influence the quality, access, and utilization of health care services.