Cancer incidence among semiconductor and storage device manufacturing workers
This dissertation had two central goals. The first was to examine and clarify methodologic issues related to retrospective follow-up studies of cancer incidence among occupational groups in the United States. The second was to determine if employment factors were associated with the incidence of any type of cancer among 89,054 International Business Machines employees at a semiconductor facility and a storage device facility.
We used data from studies of microelectronics industry employees to assess methods for developing residential histories, which are required for a cancer incidence investigation, and to determine the relative informativeness of cancer incidence and mortality studies. Use of postemployment residential histories increased person-years by up to 62% and increased the observed number of cancers by up to 28%. The number of observed cancer cases in the incidence study was 60% higher than the number of observed cancer deaths in the mortality study.
We compared employees' incidence rates with general population rates and examined incidence patterns by facility, duration of employment, time since first employment, potential for exposure to workplace environments other than offices, and work activity. Employees had lower than expected incidence for all cancers combined (2,860 observed cases, standardized incidence ratio = 84, 95% confidence interval = 81–87). Analysis of incidence patterns by potential exposure and by years spent and time since starting in specific work activities did not provide strong or consistent evidence of causal associations with employment factors.
Assumptions about residential history had little impact on validity in the incidence study. Despite geographic and temporal restrictions, incidence studies provide more data than mortality studies on cancers with good survival. Employees had fewer than expected cases of cancer compared to general populations. Incidence was increased for several cancers in some employee groups, but interpretation of these results was difficult because data on employees with long potential induction time and many years worked were sparse and because of potential confounding by nonoccupational risk factors, imprecision, and other limitations. There was no strong and consistent evidence that any form of cancer was associated causally with employment factors.
0354: Occupational safety