Purpose: Smoking, obesity, and insulin resistance are well-known risk factors for cancer, yet few epidemiology studies evaluate their role as risk factors for a second primary cancer (SPC).
Patients and methods: We identified 14,181 men with a first cancer from the National Health Insurance Corporation Study cohort. We obtained data on fasting glucose level, body mass index (BMI), and smoking history from an enrollment interview (1996). We obtained SPC incidence data for 1996 through 2002 from the Korean Central Cancer Registry. We used the standard Poisson regression model to estimate the age- and multivariate-adjusted relative risk (RR) for SPCs in relation to smoking history, BMI, and insulin resistance before diagnosis.
Results: We observed 204 patients with SPC. The overall age-standardized incidence rate of SPC was 603.2 occurrences per 100,000 person-years, which was about 2.3 times higher than that of first cancer in the general male population. Multivariate regression revealed that lung (RR, 3.69; 95% CI, 1.35 to 10.09) and smoking-related (RR, 2.02; 95% CI, 1.02 to 4.03) SPCs were significantly associated with smoking. Obese patients (BMI > or = 25 kg/m2) had significantly elevated RRs for colorectal (RR, 3.45; 95% CI, 1.50 to 7.93) and genitourinary (RR, 3.61; 95% CI, 1.36 to 9.54) SPCs. Patients with a fasting serum glucose concentration > or = 126 mg/dL had a higher RR for hepatopancreatobiliary (RR, 3.33; 95% CI, 1.33 to 8.37) and smoking-related (1.93; 95% CI, 1.01 to 3.68) SPCs.
Conclusion: Prediagnosis smoking history, obesity, and insulin resistance were risk factors for several SPCs. These findings suggest that more thorough surveillance and screening for SPCs is needed for the cancer survivors with these risk factors.