Familial aggregation of breast cancer with early onset lung cancer

Site-specific familial aggregation and evidence supporting Mendelian codomi nant inheritance have been shown in lung cancer. In characterizing lung can cer families, a number of other cancers have been observed. The current stu dy evaluates whether first-degree relatives of early onset lung cancer case s are at increased risk of breast cancer. Families were identified through population-based lung cancer cases and controls under 40 years of age. Case s were ascertained through the Metropolitan Detroit SEER registry; controls through random-digit dialing. Data were available for 384 female relatives of 118 cases and 465 female relatives of 161 controls. Breast cancer in re latives was evaluated after adjusting for age, race, sex, and smoking statu s of each family member and the sex and age of the probands. A positive fam ily history of early onset lung cancer increased breast cancer risk among f irst-degree relatives 5.1-fold (95% CI, 1.7-15.1). Relatives of cases with adenocarcinoma of the lung were at highest risk (RR = 6.3, 95% CI 2.0-20). Mean age of breast cancer diagnosis among relatives of cases was 52.2 years and not statistically different from relatives of controls. Three case fam ilies also reported early ovarian cancers (mean age of diagnosis of 35 year s). These findings suggest that shared susceptibility genes may act to incr ease risk of early onset lung and breast cancer in families. Genet. Epidemi ol. 17:274-284, 1999. (C) 1999 Wiley-Liss, Inc.