Tobacco and Public Health - TCSC Indonesia

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SMOKING AND STOMACH CANCER
residents of Taiwan (Liaw and Chen 1998), Cancer Prevention Study II (Chao et al.
2002). In four cohort studies the increase in the risk associated with smoking was statistically
not significant (Kato et al. 1992b;Guo et al. 1994; Engeland et al. 1996; Yuan et al.
1996). Three studies did not find any association between smoking and stomach cancer
(Chen et al. 1997; Nordlund et al. 1997; Terry et al. 1998).
In seven of the positive cohort studies dose–response relationships were observed
between intensity, and/or duration of smoking and the risk of cancer of the stomach.
Statistically significant trends between number of cigarettes smoked per day and
the risk of stomach cancer were observed in a 16-year follow-up report of Japanese six
prefecture study (P for trend < 0.01) (Akiba and Hirayma 1990), a 20-year follow-up
report of the cohort of US Veterans (P for trend < 0.01) (McLaughlin et al. 1995), in a
20-year follow-up report of the cohort of American men of Scandinavian and German
origin (P for trend 0.01) (Kneller et al. 1991), in a 40-year follow-up report of the cohort
of British doctors (P for trend < 0.01) (Doll et al. 1994), and in the cohort of inhabitants
of Taiwan (P for trend < 0.06) (Liaw and Chen 1998). In Cancer Prevention Study II
there was a statistically significant trend between number of cigarettes smoked per day
and the risk of stomach cancer among current smoking women (P for trend = 0.04)
and among ex-smoker men (P for trend = 0.06). The association between duration
of smoking and the risk of stomach cancer were reported by Nomura et al. (1990),
MacLaughlin et al. (1995), Liaw and Chen (1998), and Chao et al. (2002), with a statistically
significant trend between number of years smoked and the increase in relative
risk. Age started smoking was significantly associated with the risk of stomach cancer
in the cohort of American men of Japanese ancestry (P for trend < 0.0001) (Nomura
et al. 1995), in the cohort of the inhabitants of Taiwan (P for trend < 0.02) (Liaw and
Chen 1998) and among men in Cancer Prevention Study II (P for trend = 0.03) (Chao
et al. 2002). Cumulative exposure to smoking expressed as number of pack-years
of smoking has also been found to influence the risk of stomach cancer (Kneller et al.
1991; Chao et al. 2002). Cancer Prevention Study II examined the effect of cessation
on the risk of gastric cancer. Among men there was a dose–response relationship
between age-quit smoking (P for trend = 0.0015), number of years since smoking
cessation (P for trend = 0.0015), and relative risk of gastric cancer (Chao et al. 2002).
It should be noted that in most if not all studies the cohorts were followed passively
and the information on smoking habit of cohort members was based only on the interview
at the initial survey, while many cohort members could change their smoking
habit during the long follow-up period. Therefore the risk of stomach cancer associated
with smoking in these cohort studies could be underestimated due to misclassification
of former smokers as current smokers.
About 40 case–control studies investigated the association between tobacco smoking
and stomach cancer. One of them was a retrospective mortality case-referent study
(Liu et al. 1998). Nineteen studies were population-based and the rest hospital-based
case–control studies. In most studies relative risks were adjusted for different variables,