Purpose: The magnitude and timing of the reported decrease in risk of renal cell carcinoma (RCC) attributed to smoking cessation is not well characterized. Furthermore, conclusions from previous investigations have been hampered by unstable risk estimates, broad exposure categories and/or insufficient adjustment for the inverse correlation of cessation years with lifetime smoking exposure.
Methods: To address these issues, we report data from a population-based case-control study conducted in Iowa from 1986 to 1989. RCC cases (n = 387) were identified through the Iowa Cancer Registry, while controls (n = 2,333) were randomly selected from the general population, frequency-matched on age and sex. Subjects provided detailed information on a mailed questionnaire regarding their smoking history as well as other anthropometric, lifestyle, dietary and medical history risk factors.
Results: Smoothing spline regression analysis provided evidence of a consistent inverse linear trend between years of cessation and risk of RCC. In categorical analysis, compared with current smokers, those quitting > or =30 years ago experienced a 50% reduction in risk of RCC (OR = 0.5; 95% CI 0.3 to 0.8) after adjustment for age, sex, BMI, hypertension and pack-years of smoking. Risk among long-term quitters was similar to risk among never smokers (OR = 0.6; 95% CI 0.4 to 0.8). In contrast, cessation of <10 years, 10 to 19 years and 20 to 29 years all resulted in a less pronounced reduction in RCC risk ( approximately 20% to 30%).
Conclusions: Our findings suggest that while cessation of smoking is indeed associated with a linear decrease in RCC risk even after adjustment for potential confounders, this benefit may not be sizeable until more than 20 years following cessation.