Modelling the relative risk of esophageal cancer in a case-control study

The aim of this paper was to evaluate the combined effect of alcohol, smoking habits and frequency of consumption of selected dietary items, which are the major sources of retinoids and beta-carotene in the Italian diet, on the risk of esophageal cancer (EC). The adequacy of the multiplicative structure for describing the effect of these factors on risk was examined. The analysis was carried out using the Breslow and Storer family of relative risk functions to assess which scale, between the subadditive and the supermultiplicative, could better explain the risk structure underlying the data. Data from a case-control study including 211 males with EC and 712 controls were analyzed. Data were collected in teaching and general hospitals of the greater Milan area (Italy). Under the multiplicative model, consistent with the results obtained in other studies, alcohol and tobacco consumption increased the risk of EC. There was no significant association between the retinol index and the risk of EC, while the beta-carotene index showed a protective effect. Using the Breslow and Storer family it was possible to rule out the additive model as an adequate one to describe the relative risk. The results suggest that the combined effect of alcohol, smoking and beta-carotene intake is near to multiplicative. A larger data set and perhaps more detailed data on risk factors are needed to discriminate among models near the multiplicative one. Important implications on causal interpretation and public health practice may derive from this type of analysis.