Tobacco and Public Health - TCSC Indonesia

TONGZHANG ZHENG ET AL. 411
the control group selected represents the population that produced the cases. Indeed,
in some of the hospital-based case–control studies, the control group considered
included cancers thought to be unrelated to smoking and drinking, and some with
benign neoplastic or non-neoplastic lesions, which may be smoking related. If it turns
out that these diseases were actually associated with tobacco smoking, then, the true
relationship between tobacco smoking and oral cancer risk would be underestimated.
Since most of these studies showed a strong association between cigarette smoking and
oral cancer risk, underestimation is less of a concern. But the variation of disease in
controls in different studies is still important to note as when considered together with
the relatively small sample size in some of the studies, it may explain in large part, the
significant variation in the magnitude of the reported association between tobacco
smoking and oral cancer risk.
In 1984, Elwood et al.reported an alcohol-adjusted OR of 2.8 (95% CI 1.3–6.0) for
smoking 50 or more cigarettes per day when compared to never smokers. Additional
adjustment for 4 other factors reduced the OR to 2.1 (95% CI 0.9–4.8). A weak association
observed in this study could be due to the fact that controls were composed of
various cancer patients (including cancer of the prostate, colo-rectum, skin, breast, etc.).
In a case–control study of oral cancer in Brazil, Franco et al. (1989) reported that
tobacco smoking was, by any measure, the strongest risk factor for oral cancer in this
population. The adjusted ORs for ever vs. never smokers were 6.3 (95% CI 2.4–16.3),
5.5 (95% CI 1.2–24.8), 13.9 (95% CI 4.4–44.2), and 7.0 (95% CI 2.7–18.7) for industrial
brand cigarettes, cigars, pipe, and hand-rolled cigarettes, respectively. The OR for the
heaviest vs. the lowest consumption categories (>100 vs. 49 pack-years when compared to non-smokers. In
females, the corresponding values were 1.5 (95% CI 0.4–5.1) and 12.0 (95% CI
3.8–38.0), respectively. Site-specific analysis for males also showed a significant
increase with increasing pack-years of cigarette smoking for cancer of the larynx
(P trend < 0.01), tongue (P trend < 0.01), and floor of mouth (P trend = 0.02), but not for
orohypopharynx (P trend = 0.13), and other oral cavity (P trend = 0.15). A significant risk
reduction was observed after 15 or more years of smoking cessation.
Zheng et al. (1990) conducted a case–control study of oral cancer in Beijing, China,
including 404 histologically confirmed incident cases and an equal number of hospitalbased
controls. The study reported an alcohol-adjusted OR of 2.4 (95% CI 1.5–4.0) for
male smokers when compared to never smokers. Three measures of level of exposure—
cigarette equivalents smoked per day, years smoked, and lifetime pack-years of
smoking—all showed highly significant exposure–response relationships (P trend < 0.001).