Objective: To evaluate the association between cigarette smoking and risk of primary liver cancer (PLC) among middle-aged and elderly men in urban Shanghai.
Methods: A nested case-control study was conducted based on a cohort of 18,244 men who were 45-64 years of age in 1986-1989 and had no history of cancer at recruitment in Shanghai. As of 31 Dec 2000, a total of 213 incident cases of PLC were identified. 1094 matched controls were randomly selected among the cohort subjects who were free of cancer and alive at the time of cancer diagnosis of the index case. The matching criteria were date of birth (within 2 years), date of biospsy specimen collection (within 1 month), and neighborhood of residence at recruitment. Conditional logistic regression models were used to estimate adjusted odds ratios (ORs) and their corresponding 95% confidence intervals (CIs).
Results: After controlling for potential confounders, cigarette smoking (ever vs. never) was associated with risk of PLC (OR = 1.91; 95% CI: 1.28-2.86). Risk of PLC increased with increasing number of cigarettes smoked per day, as well as duration of cigarette smoking, pack-years of cigarettes consumed over lifetime and earlier age started smoking. The ORs were 2.16 (95% CI = 1.37-3.40), 2.14 (95% CI = 1.18-3.87), 2.12 (95% CI = 1.21-3.74) and 2.57 (95% CI = 1.50-4.40) for men who smoked 20 cigarettes or more daily, smoked for 40 or more years, consumed more than 37 pack-years of cigarettes, and began smoking before 20 years of age, respectively.
Conclusion: This study confirms that cigarette smoking is an independent risk factor for primary liver cancer among males in Shanghai.