Cigarette smoking and renal cell carcinoma risk among black and white Americans: effect modification by hypertension and obesity.

BACKGROUND: Incidence of kidney cancer has been increasing over the past three decades, with more rapid increases and higher incidence rates among blacks than whites in the United States. An association between cigarette smoking and renal cell carcinoma (RCC), the most common form of kidney cancer, has been reported for whites, but the association in blacks is less clear.
METHODS: The association between smoking and RCC was examined in 1,217 incident cases and 1,235 population controls frequency-matched on age, race, gender, and study site in the Kidney Cancer Study in Detroit, MI, and Chicago, IL.
RESULTS: In white individuals, increasing duration and number of pack-years of both were associated with increased risk of RCCs after adjusting for age, gender, education, study site, body mass index (BMI) and history of hypertension (P(trend) = 0.0002 and P(trend) = 0.002, respectively). Among black individuals, RCC risk increased with duration of smoking (P(trend) = 0.02) but not other measures. Compared with current smokers, RCC risk decreased with increasing years of smoking cessation among both whites and blacks (P(trend) = 0.01 and 0.02, respectively). When examining risk according to hypertension history, associations between smoking and RCC risk were observed only among individuals who reported never having been diagnosed with hypertension. Similarly, cigarette smoking was associated with increased risk of RCCs among nonobese individuals but not among those with BMI ≥ 30 kg/m(2).
CONCLUSION: Our observation that smoking is associated with RCC only in nonobese individuals and those with no history of hypertension are novel findings. IMPACT: The complex relationships between RCCs, smoking, hypertension, and obesity require additional confirmation.