Family history of cancer and risk of lung cancer in lifetime non-smokers and long-term ex-smokers

Background. Genetic factors appear to play a role in the aetiology of lung cancer. Methods. To examine the association between family history of cancer (all types) and risk of lung cancer among nonsmokers, we conducted a case-control study. Cases (n = 618) were identified through the Missouri Cancer Registry for the period 1986 through 1991, and included 432 lifetime non-smokers and 186 ex-smokers who had stopped at least 15 years prior to diagnosis or had smoked for less than one pack-year. Controls (n = 1402) were selected through drivers licence and Medicare files. Results. The risk of lung cancer increased directly in relation to the number of family members affected with cancer. The odds ratio (OR) associated with five or more first-degree relatives with cancer was 2.7 (95% confidence interval [Cl]: 1.2-6.1), with a significant linear trend in risk according to the number of relatives affected (P = 0.03). Increased lung cancer risk was associated with two or more affected siblings (OR = 1.4; 95% Cl: 1.0-1.9) and with two or more affected offspring (OR = 3.2; 95% Cl: 1.3-8.1). Risk was slightly elevated for family history of lung cancer (OR = 1.3; 95% Cl: 1.0-1.8). Conclusions. Our study identified a slight increase in risk of lung cancer in relation to five or more relatives with cancer. Preventive implications of this increased risk are unclear because the attributable fraction is low in comparison to a variety of other factors.