Tobacco and Public Health - TCSC Indonesia

TONGZHANG ZHENG ET AL. 413
For smokers of unfiltered cigarettes, the ORs were 7.8 (95% CI 2.4–19.0), 7.7
(3.6–16.5), 12.3 (5.3–28.6), and 7.6 (3.5–16.8) for consumption of 6 to 15, 16 to 25,
26 to 35, and 36 or more cigarettes per day, respectively. The corresponding ORs for
smokers of filtered cigarettes were 1.5 (0.5–4.2), 3.6 (1.6–7.7), 1.9 (0.7–5.0), and 2.3
(1.0–5.2), respectively. Using the same dataset, Boffetta et al. (1992) showed that soft
palate had the highest ORs associated with tobacco smoking (OR = 4.9, 95% CI
1.1–21.5 for those smoking more than 35 cigarettes per day). A similar susceptibility to
tobacco was shown for floor of the mouth (OR = 4.0, 95% CI 1.5–10.3, P trend < 0.01 for
those smoking more than 35 cigarettes per day). A stronger effect of tobacco on
posterior sites of the oral cavity, such as soft palate, is consistent with the earlier studies
by Hirayama (1966) and by Jussawalla and Deshpande (1971).
Kabat et al. (1994) reported a large hospital-based case–control study in eight US
cities, involving 1560 histologically incident cases of oral and pharyngeal cancer and
2948 controls (including both cancerous and non-cancerous controls). The study
found that the OR for oral cancer was significantly increased in current smokers for
both males (OR = 3.3, 95% CI 2.4–4.3) and females (OR = 4.3, 95% CI 3.2–5.9). Among
current smokers of both sexes the OR increased with amount of smoking, and among
ever smokers the risk increased with duration of smoking. Compared to lifetime
non-filter smokers, lifetime filter smokers or those who switched to filter cigarettes had
a reduced risk of oral cancer. Quitting smoking was associated with a substantial
reduction of cancer risk which was evident even in the first few years following cessation.
Macfarlane et al. (1995) also reported a higher risk of female smokers from tobacco
smoking in a combined analysis of three case–control studies from China, US, and
Italy. They found that, among men, the ORs were 1.7 (95% CI 1.2–2.5) for those who
smoked 33 pack-years or less, and 3.8 (95% CI 2.5–5.8) for those who smoked more
than 33 pack years. Among women, the corresponding ORs were 2.7 (95% CI 1.6–4.7)
and 6.2 (95% CI 3.4–11.2), respectively. The large sample size of the combined analysis
allowed the authors to examine the risk associated with smoking among never alcohol
drinkers. They reported that, among those who never consumed alcohol, the risk of oral
cancer increased with increasing consumption of tobacco and the risk again was found
to be higher for females amongst whom the increases were statistically significant.
Smoking cessation resulted in a significant risk reduction, those who had stopped smoking
for more than 9 years had a risk half that of current smokers (OR = 0.5, 95% CI 0.3–0.7).
In a case–control study of 1009 oral cancer patients and 923 age-matched controls in
the US, Muscat et al. (1996) not only found a significant dose-response relationship
between oral cancer risk and lifetime cumulative tar intake (P trend < 0.01) or lifetime
pack-years of smoking (P trend < 0.01), they also reported a significant gender difference
in the smoking-related risks for oral cancer. For example, the adjusted OR for men,
according to increasing quartile of cumulative lifetime tar consumption and relative to
never smokers, was 1.0, 0.9, 1.6, and 2.1. Among women, the corresponding ORs were
1.8, 2.8, 3.2, and 4.6.