Objectives: A case-control study within a cohort of the workers employed by Electricité 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 career points.
Methods: All the incident cases of breast cancer in women and all the incident cases of upper respiratory and digestive tract cancer (comprising cancers of the larynx, pharynx, buccal cavity and esophagus), lung cancer, hematopoietic system cancers and colon cancer in men were extracted from the Cancer Register of the Social Security Department. The controls were matched for age (men) and for age and length of employment in the company (women). Socioeconomic status was measured at three professional career points (beginning, midpoint (about 35), and time of diagnosis (about 48)) by two types of socio-professional variables: employee category (low, medium, high) and a variable based on the French socioeconomic status classification system. An estimation of social mobility was done between career beginning and midpoint. 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 start than later in the career for breast cancer in women. The category of operations staff was used as a reference, and this analysis shows a difference between the risks associated with supervisors (OR = 2.0) and managers and 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 odds ratio was 3.4 for supervisors, 7.8 for operations staff and 14.8 for production staff. There was a socioeconomic gradient in lung cancer at all points in the career and in the incidence of the hematopoietic system cancers at 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 there is a social gradient in the incidence of a cancer, an individual's social change is at least as important as his/her original social status in the relationship between cancer and social class.