These results support the hypothesis that socioeconomic and geographical environment influences prognosis of digestive cancer in France, as previously found in other European countries and in the USA (Woods et al, 2006
). This influence appears to be significant for the most common cancers with better prognosis (colon, rectum), and to a lesser extent for cancers with poorer prognosis (oesophagus, stomach, liver and pancreas). No influence was found for gall bladder and biliary tract cancer.
Certain methodological aspects of our study are relevant. In the absence of individual-based social information, the surrogate of an aggregate (Commune level) social indicator was used. Moreover, no deprivation index is available in France, prompting a multidimensional approach to poverty (remote patient; education; income; working conditions and accommodation).
The level of geographical unit used in our study was the Commune
s are the smallest administrative unit in France but their population sizes vary widely. The National Institute for Statistics and Economic Studies (INSEE) has defined a smaller unit: ‘Ilots regroupés d'indice statistique' (IRIS). Regional capital and other important Commune
s are divided into several IRIS and small Commune
s constitute one IRIS. Therefore, the use of IRIS increases the accuracy of socioeconomic variables in such studies (Woods et al, 2005
). Unfortunately, the lack of information on patients' addresses prevented us from using the IRIS in our study. Socioeconomic inequalities highlighted in our study are likely to have been increased had we used the IRIS unit.
The use of relative survival, instead of crude survival, would have enabled us to adjust for comorbidity associated with age and gender, but to our knowledge, no multilevel relative survival model is available. As recently stressed (Auvinen and Karjalainen, 1997
), relative survival tends to underestimate social inequalities in survival so we have preferred multilevel analysis rather than specific mortality.
The present study suffers from the lack of information on change in Census data during the study period. In fact, aggregate variables were collected in 1999 by the French Census and in 2003 for income tax purposes in an annual survey by the Direction Générale des Impôts, the tax department. The National Institute for Statistics and Economic Studies does not organise a Census each year. Furthermore, since multiple comparisons were made (six factors were tested for each of the eight cancers), some tests (two or three) may be significant by chance.
Nevertheless, our results accord with previous studies that stressed the appreciable gap between the most deprived and the most affluent in survival (Woods et al, 2006
). At least in England and Wales, this was more widespread in the 1990s than previously (Coleman et al, 2004
). In France, two studies, based on small samples, demonstrated that Communes
with a high proportion of dwellings without bath or shower were negatively correlated with cancer survival (Monnet et al, 1993
) and that farmers of both sexes and unemployed men had poorer survival than other socioeconomic categories (Desoubeaux et al, 1997
). The frequent association of this housing measure suggested that it was a relevant socioeconomic indicator.
For cancers with good prognosis, in our study, the influence of socioeconomic aggregate variables on survival were similar to those in a Norwegian population-based study also using multilevel survival (discrete-time hazard regression) (Kravdal, 2006
). In the Norwegian study, education variables (at individual and community level) were the most relevant socioeconomic indicators.
In our study, unlike the Norwegian study (Kravdal, 2006
), road distance between cancer centres and the Commune
of residence is a predictor of cancer survival for almost half of the cancer sites. This contradiction between the two studies may be partially explained by the adjustment for cancer stage at diagnosis in the Norwegian study. Lack of information on stage at diagnosis in our study restricts the interpretation of our results. Cancer stage at diagnosis is often more advanced in deprived people (Ionescu et al, 1998
; Ciconne et al, 2000
), although one recent study (Brewster et al, 2001
) failed to find this for colorectal cancer using Carstairs deprivation categories. The explanation of social inequalities in cancer survival by the difference in stage at diagnosis is attractive as a consequence of the importance of stage at diagnosis as a prognostic factor. Nevertheless, as underlined by a recent review (Woods et al, 2006
), stage at diagnosis does not entirely account for the gap in cancer survival between the most deprived and the most affluent.
Although geographic and socioeconomic effects on prognosis are modest compared to clinical prognostic factors such as histology or stage at diagnosis, they warrant consideration as potential survival predictors in digestive tract cancer. Few such studies have been carried out, partly due to the lack of individual-based information. Our study implies that the French health-care system, which theoretically provides free access to care to all patients, with extensive hospital services throughout the country, does not prevent social inequalities in cancer management.