© 2005 Foundation for Promotion of Cancer Research
Trends in Lung Cancer Mortality Among Young Adults in Japan
1 Statistics and Cancer Control Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, 2 Division of Mathematics, School of Medicine, Liberal Arts and Sciences, Sapporo Medical University, Sapporo and 3 Epidemiology and Health Promotion, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan
For reprints and all correspondence: Tomomi Marugame, Statistics and Cancer Control Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. E-mail: tmarugam{at}gan2.res.ncc.go.jp
Received July 26, 2004; accepted January 19, 2005
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Abstract |
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Background: Trends in lung cancer mortality among young adults, which are important for projecting future trends, have not been explored previously in Japan.
Methods: Using data from the National Vital Statistics between 1958 and 2003, we compiled lung cancer mortality by sex and 5-year birth cohort among young adults aged 20–49.
Results: Mortality among those aged 20–29 has consistently decreased regardless of sex. There were birth cohort effects in mortality from lung cancer, although these were less evident among women than among men. Both men and women born in the 1930s had lower mortality rates, while those born after 1940 had higher lung cancer mortality rates. Mortality rates appear to be declining for male birth cohorts born after 1950 and female birth cohorts after 1960, although these trends may not be stable due to the small number of deaths in these cohorts.
Conclusion: Lung cancer mortality trends appear to be decreasing among young adults. This might be associated with the lower mortality of birth cohorts after 1950 for men and the 1960s birth cohorts for women. Careful monitoring is needed to confirm continuation of these declining trends.
Key Words: lung cancer • mortality • young adults • Japan
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INTRODUCTION |
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Mortality trends from lung cancer showed a drastic increase in the 20th century in Japan. However, different birth cohorts have lower or higher rates of mortality of lung cancer (1,2). The resulting birth cohort effects, which are unique to Japan, affect the national trends for lung cancer mortality. Previous studies, however, have mainly focused on lung cancer mortality among individuals
50 years of age. Although young adults are less prone to develop lung cancer, lung cancer trends among them are important for forecasting future lung cancer mortality trends when they reach the ages of these older groups (3,4). The aim of the present study was to evaluate trends of lung cancer mortality in Japan, especially focusing on mortality trends by birth cohorts among young adults between 20 and 49 years of age during the period of 1958–2003.
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SUBJECTS AND METHODS |
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The number of deaths due to lung cancer was obtained from the National Vital Statistics for the years between 1958 and 2003. The International Classification of Diseases (ICD) code corresponding to lung cancer was 162 and 163 in the 7th revision (1960–1967), 162 in the 8th and 9th revisions (1968–1978 and 1979–1994, respectively), and C33 and C34 in the 10th revision (1995–2003). Based on the Japanese population of 1958–2003, we calculated the lung cancer mortality rates per 100 000 for every year of the observation period by sex and 5-year age group from 20 to 49. We then presented age-specific lung cancer mortality rates for these birth cohorts. The birth cohort year was defined as the year when the death occurred minus the middle age of a 5-year age group. Details of the calculation of age- and birth cohort-specific lung cancer death rates have been described elsewhere (5).
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RESULTS |
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Decreasing trends in mortality from lung cancer during the last 30 years were observed for the 20–29 age groups regardless of sex (Fig. 1A) although mortality rates were not stable because of the small number of deaths. For men aged 30–49 years, an increasing trend was observed after 1958, then mortality rates appeared to decline after 1980. The peak of lung cancer mortality in each age group seemed to occur earlier in the group aged 30–34 than in the group aged 45–49. Among women aged 30–34, the mortality from lung cancer was almost constant (Fig. 1B) but tended to increase after 1958 among women aged 35–49. Although the peak was not as evident as in men, a declining trend seemed to appear at around 2000.
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When we focused on lung cancer mortality rate by birth cohorts, the observed increases among men in the birth cohorts before 1930 clearly diminished for the 1930s birth cohorts (Fig. 2A). However, mortality from lung cancer increased with successive birth cohorts after the 1940s birth cohorts. The peak of elevation seemed to appear in the 1950s birth cohorts, but this group included only individuals from 20 to 44 years of age. Among successive birth cohorts born after 1960, the mortality rates of lung cancer gradually decreased. Like men, women born in the late 1920s to 1930s had lower lung cancer mortality rates (Fig. 2B). Successive birth cohorts of women born in the 1940s and early 1950s had gradually increasing mortality for lung cancer. None of the birth cohorts showed a definite peak, but the mortality rates among the successive birth cohorts born after around 1960 may be beginning to decline.
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DISCUSSION |
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The lung cancer mortality data from 1958–2003 suggest a birth cohort effect in the mortality rate from lung cancer among young Japanese men and women aged 20–49. Lung cancer mortality increases among men for successive birth cohorts born before 1930, then is flat for successive birth cohorts in the 1930s, and finally increases again for successive cohorts born after the 1940s, with a peak among the 1950s cohorts. For women, the mortality rate was lower among 1930s birth cohorts, but it increased for those born after 1940. Although it was less evident than in men, a possible decline in lung cancer mortality was observed among women born after around 1960.
Birth cohort effects in the lung cancer mortality rates from 1952 to 2001 have been observed among Japanese men and women aged 50 (1). Men born between 1933 and 1941 and women born between 1923 and 1931 reportedly have lower lung cancer mortality rates (1). Among successive birth cohorts born in the 1940s, the mortality rates of lung cancer increased for both men and women. These trends were also detected among young adults aged 30–49 in the present study.
These observations indicate the importance of a birth cohort effect for interpreting and forecasting national trends for lung cancer mortality. It has been projected that the national lung cancer burden (in terms of age-standardized mortality rates) might increase because those born during the 1940s (1), who have higher mortality rates from lung cancer, are entering their cancer-prone years. It will be two or more decades before the male birth cohorts born after the 1950s, with their possibly lower lung cancer mortality, will enter their cancer-prone years and influence the national lung cancer mortality.
Because there is an apparent birth cohort effect on lung cancer mortality rates (1), the national trend of lung cancer deaths should be interpreted based on smoking prevalence by birth cohorts. In Japan, however, there has been no previous analysis of smoking prevalence of successive birth cohorts.
In contrast to trends in the other age groups, the 20–29 age groups (both men and women) showed declining lung cancer mortality during the last 30 years. According to data from Japan Tobacco Industry, Inc., current smoking prevalence has consistently decreased among Japanese men aged 20–29. However, we have no clear explanation for the observed decline for women because current smoking prevalence has increased among women aged 20–29. If these young women had quit smoking soon after starting, then their total exposure to smoking might not have been enough to cause lung cancer; however, we have no data to substantiate this. For young adults under 50, it is debatable whether smoking is strongly associated with lung cancer because the positive association between smoking and adenocarcinoma was not very strong among young Japanese adults, and this is the most common form of lung cancer among young adults, especially women (6).
Smoking behavior by birth cohort reflected the national trends among young adults (aged 20–29) in other countries. In the USA, a slowing in the rate of decrease in lung cancer mortality was observed among young adults born after 1950. This trend reflected starting cigarette smoking at an earlier age (4). Although smoking, especially among women in their 20s, increased markedly in Japan, this increase in smoking prevalence did not parallel the cancer mortality trends, at least among women aged 20–29.
In conclusion, there were birth cohort effects in lung cancer mortality for Japanese young adults aged 20–49. Among men, there were two peaks, one for the late 1920s cohort and the other for the 1950s birth cohort, and one trough for 1930s birth cohorts. Among women, there was one peak for the late 1950s or early 1960s birth cohorts. For men and women born after 1960, lung cancer mortality rates seemed to decline, although this was not as evident among women as among men. Because national trends are closely associated with birth cohort effects, careful monitoring is needed to establish that this is a true decline.
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References |
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TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
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1 Kaneko S, Ishikawa KB, Yoshimi I, Marugame T, Hamashima C, Kamo K, et al. Projection of lung cancer mortality in Japan. Cancer Sci 2003;94:919–23.[CrossRef][Medline]
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3 Strand TE, Malayeri C, Eskonsipo PK, Grimsrud TK, Norstein J, Grotmol T. Adolescent smoking and trends in lung cancer incidence among young adults in Norway 1954–1998. Cancer Causes Control 2004;15:27–33.[CrossRef][ISI][Medline]
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5 Yoshimi I, Sobue T. Mortality trend in Japan (1960–2000): with special reference to birth cohort: all sites. Jpn J Clin Oncol 2004;34:360–8.
6 Marugame T, Kamo K, Sobue T, Akiba S, Mizuno S, Tamakoshi A, et al. Trends in smoking by birth cohort in Japan. Cancer Sci 2004;95 (Suppl):542.
7 Tsugane S, Watanabe S, Sugimura H, Arimoto H, Shimosato Y, Suemasu K. Smoking, occupation and family history in lung cancer patients under fifty years of age. Jpn J Clin Oncol 1987;17:309–17.
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