Background: The high incidence of oesophageal cancer in northern China is attributed predominantly to environmental factors. The role of genetic factors has not been extensively studied.
Methods: Our aim was to study familial aggregation of oesophageal cancer in pedigrees from a defined population base in a high incidence area in China and to quantify the risk associated with different first degree relatives using different analytical approaches. Detailed data on family members of three successive generations and the occurrence of oesophageal and other cancers in family members were collected from a population-based series of 244 oesophageal cancer cases which occurred between 1987 and mid-1992 in Huixian County, Henan.
Results: Compared to expected rates, the standardized mortality ratio (SMR) of oesophageal cancer among first degree relatives of oesophageal cancer patients was 2.4 (2.2 in male and 2.7 in female relatives). The corresponding SMR for first and second degree relatives were 1.6 and 2.2. The null hypothesis of 'no familial aggregation' was rejected using Tarone's one-sided score test for binomial distributions indicating some evidence for clustering within families. To account for variance due to between-pairs correlation and family and/or individual specific variables, we fitted a series of regression models using a Generalized Estimation Equations (GEE) approach. The pairwise odds ratios were 2.3 for parent-parent, 1.9 for sib-parent and 1.1 for sib-sib, adjusted for sex, age and sex of index case.
Discussion: The existence of familial aggregation of oesophageal cancer in the study population was confirmed using different analyses and a two- to threefold increased risk was found for first degree relatives. The clear association of disease between parent and sib provides some indication of a genetic component. The pairwise association between parents but not between sibs suggests that environmental factors have a stronger action after childhood.