Socioeconomic status, social mobility and cancer occurrence during workinglife: a case-control study among French electricity and gas workers

Objectives: A case-control study within a cohort of the workers employed by Electricite de France and Gaz de France between 1988 and 1992 was carried out to investigate relationships between cancers and socioeconomic status, including the effects of social mobility, by studying three professional ca reer points. Methods: All the incident cases of breast cancer in women and all the incid ent cases of upper respiratory and digestive tract cancer (comprising cance rs of the larynx, pharynx, buccal cavity and esophagus), lung cancer, hemat opoietic system cancers and colon cancer in men were extracted from the Can cer Register of the Social Security Department. The controls were matched f or age (men) and for age and length of employment in the company (women). S ocioeconomic status was measured at three professional career points (begin ning, midpoint (about 35), and time of diagnosis (about 48)) by two types o f socio-professional variables: employee category (low, medium, high) and a variable based on the French socioeconomic status classification system. A n estimation of social mobility was done between career beginning and midpo int. Cases and controls were compared for socioeconomic status at the three career points. They were also compared for social mobility. Results: The differences between the social categories were larger at the s tart than later in the career for breast cancer in women. The category of o perations staff was used as a reference, and this analysis shows a differen ce between the risks associated with supervisors (OR = 2.0) and managers an d specialist professions (OR = 1.5). There were large differences according to the type of cancer in men. A socioeconomic gradient in the incidence of cancers of the upper respiratory and digestive tract was observed at every career stage. The gradient was largest at the moment of diagnosis. The odd s ratio was 3.4 for supervisors, 7.8 for operations staff and 14.8 for prod uction staff. There was a socioeconomic gradient in lung cancer at all poin ts in the career and in the incidence of the hematopoietic system cancers a t mid-career and at diagnosis. No association between socioeconomic status and colon cancer was found. Social mobility accentuated all these results. Conclusion: Socioeconomic status is involved in the development of cancers. Our study suggests that the transition from social to biological processes could act via specific lifestyle and/or work-related risk factors. When th ere is a social gradient in the incidence of a cancer, an individual's soci al change is at least as important as his/her original social status in the relationship between cancer and social class.