title: Familial cancer aggregation and the risk of lung cancer.
abstract: BACKGROUND
  Around 90% of lung cancer worldwide is attributable to cigarette smoking, although less than 20% of cigarette smokers develop lung cancer. Other factors such as diet, chronic lung diseases, occupation and possibly environmental agents also contribute to this cancer. Genetic factors seem to play a role in lung cancer, but the precise characteristics influencing lung cancer susceptibility are not known, since genetic factors are easily obscured by the strong environmental determinants of lung cancer, particularly smoking.
  
  
  OBJECTIVE
  To estimate the effect that cancer occurrence among first-degree relatives has on the risk of lung cancer.
  
  
  METHODS
  Hospital-based case-control study.
  
  
  METHODS
  The metropolitan region of São Paulo, Brazil.
  
  
  METHODS
  334 incident lung cancer cases and 578 controls matched by hospitals.
  
  
  METHODS
  By means of a structured questionnaire, cases and controls were interviewed about cancer occurrence in first-degree relatives, tobacco smoking, exposure to passive smoking, occupation, migration and socioeconomic status. Non-conditional logistic regression was used to calculate the risk of familial cancer aggregation, the effect of cancer in first-degree relatives and smoking in conjunction, and for controlling confounders.
  
  
  RESULTS
  The adjusted odds ratio (OR) revealed a slight, but not statistically significant, excess risk of lung cancer for subjects with a history of lung cancer in relatives (OR 1.21; 95% confidence interval [CI] 0.50 - 2.92). The same was found among those with a history of other tobacco-related cancers in relatives (OR 1.36; 95% CI 0.87 - 2.14). A step gradient effect was observed regarding lung cancer risk, in accordance with increases in the number of pack-years of cigarette consumption. An interaction between familial cancer aggregation and tobacco smoking was detected.
  
  
  CONCLUSIONS
  A mildly elevated risk of lung cancer among persons with a positive history of lung and other tobacco-related cancers was observed. The finding of an interaction between the variables of familial cancer aggregation and smoking suggests that familial cancer aggregation could be considered as a marker of susceptibility, increasing the risk of lung cancer among smokers. These results improve our knowledge of lung carcinogenesis and can guide future cancer genetic studies.
authors: Department of Epidemiology, Public Health School, University of São Paulo, São Paulo, Brazil. wunsch@usp.br
authors: Victor
authors: V
authors: Wünsch-Filho
authors: Paolo
authors: P
authors: Boffetta
authors: Didier
authors: D
authors: Colin
authors: José Eduardo
authors: JE
authors: Moncau
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001938:Brazil / Q000453:epidemiology; D016022:Case-Control Studies; D016001:Confidence Intervals; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D008175:Lung Neoplasms / Q000453:epidemiology / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects; D014505:Urban Population