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ContextEvidence exists that lung cancer aggregates in families and recent findings of a chromosomal region linked to lung cancer susceptibility support a genetic component to risk. Family studies of early-onset lung cancer patients offer a unique opportunity to evaluate lifetime risk of lung cancer in relatives.ObjectiveTo measure lung cancer aggregation and estimate lifetime risk among relatives of early-onset cases and population-based controls.Design and SettingFamilial aggregation and cumulative risk estimates from interview data of incident cases and concurrently ascertained controls between 1990 and 2003 in metropolitan Detroit, Mich.ParticipantsThe study included 7576 biological mothers, fathers, and siblings of 692 early-onset cases and 773 frequency-matched controls. One third of the population was black.Main Outcome MeasuresCumulative lifetime risk of lung cancer, stratified by race and smoking behavior in relatives of early-onset cases and controls.ResultsSmokers with a family history of early-onset lung cancer in a first-degree relative had a higher risk of developing lung cancer with increasing age than smokers without a family history. An increase in risk occurs after age 60 years in these individuals, with 17.1% (SE 2.4%) of white case relatives and 25.1% (SE 5.8%) of black case relatives diagnosed with lung cancer by age 70 years. Relatives of black cases were at statistically significant increased risk of lung cancer compared with relatives of white cases (odds ratio, 2.07, 95% confidence interval, 1.29-3.32) after adjusting for age, sex, pack-years, pneumonia, and chronic obstructive lung disease.ConclusionsFirst-degree relatives of black individuals with early-onset lung cancer have greater risk of lung cancer than their white counterparts, and these risks are further amplified by cigarette smoking. These data provide estimates of lung cancer risk that can be used to offer counseling to family members of patients with early-onset lung cancer.