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

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.

[Cancer incidence among active female workers at Electricité de France-Gaz de France]. / Incidence des cancers chez les salariées en activité d'Electricité de France Gaz de France.

Our aim was to draw up a first general view of cancer pathology among the EDF-GDF women thanks to the cancer register among active employees created by the social security department of the French national electric and gas company EDF-GDF. Between 1978 and 1992, 764 cases of cancer were diagnosed. Breast cancer was the most common (52.4%), followed by gynaecological cancers: uterus (8.6%) and ovary (6.2%), and colon and rectum cancers (5.4%). The age-standardized breast cancer incidence using the 1978-1982 period as a basis increased over time. A higher incidence for breast cancer and a lower incidence for uterus cancer were observed among the EDF-GDF women during the 1978-1982 and 1983-1987 periods, compared to French women of same age. The study of the relationship between breast cancer risk and socioeconomic status, by means of indirect standardization, showed that the breast cancer risk increased with increasing socioeconomic status. Thus manual workers had a lower breast cancer risk than the EDF-GDF woman cohort (SIR = 0.72), foremen had the same risk (SIR = 1.05) and managers had a significantly higher risk (SIR = 1.64). Moreover a case-control study showed that the change in socioeconomic status between the beginning (20 years old) and the middle of a career (35 years old) was important but it was essentially the socioeconomic status at the beginning which determined the breast cancer risk. The results support the hypothesis of a "social class" effect through risk factors during the first part of the life.