Working in Computer Factories May Increase Cancer Risk

BOSTON, Oct. 19 -- Building computers may bestow an increased risk of several kinds of cancer, according to an analysis of a large mortality database available.

Brain, kidney and breast cancer and non-Hodgkin's lymphoma were more common causes of death for IBM employees than the rest of the population, reported Richard W. Clapp, M.P.H., D.Sc., of Boston University, in a study published today in the open access journal Environmental Health.

Because the data were released by the company involuntarily during litigation, no information was available to link these deaths to any specific chemicals or other toxic exposures.

Cancer was a more common cause of death in the IBM employees than in the general U.S. population. The proportional mortality ratio for all cancers was 107 (107% of expected, 95% confidence interval 105 to 109) in men and 115 (95% CI 110 to 119) in women.

Among all female workers, only the proportional cancer mortality ratio for breast cancer (PCMR=115; 95% CI=106, 125) remained significantly elevated compared with its proportional mortality ratio.

The pattern of deaths was similar in men and women and similar between manufacturing workers and all workers combined, Dr. Clapp said. Significance may have been more difficult to reach in the female manufacturing worker group because of few deaths in this much smaller group (302 cancer deaths), he added.

Dr. Clapp calculated expected mortality rates for the 31,941 IBM employees whose causes of death were recorded in the database from 1969 and 2001 and had worked at the company for at least five years. He compared these to national mortality figures for 66 causes of death in males and females.

Notably, the employees were primarily males (27,272 versus 4,669 females). Work history was available for a subset of 10,219 of the deceased workers. Duplicate records were excluded as were records for which the sex, birth date, or death date remained unknown or discrepant.

The expected number of deaths was computed by multiplying the proportional mortalities from each cause in the U.S. population by the total number of deaths for each cause in the workers. The proportional mortality ratios were standardized on age, sex, and time. The standardized proportional cancer mortality ratios are less susceptible to distortion by the "healthy worker effect," Dr. Clapp said. They were calculated as a proportion of all-cancer mortality.

There were 7,697 cancer deaths in men and 1,667 in women. The average age at death was 64.5 years for male workers and 63.4 for female workers in the database. The average age at death due to cancer was 63.9 years for male employees and 59.5 for females in the database.

Among the specific malignancies looked at, Dr. Clapp found the following proportional cancer mortality ratios to be significantly elevated in male manufacturing workers compared with the proportional mortality ratios:

• Brain and central nervous system cancer (166, 95% CI 129 to 213).
• Kidney cancer (162, 95% CI 124 to 212).
• Melanoma (179, 95% CI 131 to 244).
• Pancreatic cancer (126, 95% CI 101 to157).

Among all male workers, the significant (P<0.05) proportional cancer mortality ratios were:

• Digestive organs and peritoneum (108.4, 95% CI 104.4 to 112.6),
• Large intestine (124.0, 95% CI 116.0 to 132.6),
• Pancreatic (118.5, 95% CI 108.2 to 129.8),
• Kidney (136.1, 95% CI 120.9 to 153.2),
• Malignant melanoma (159.9, 95% CI 140.6 to 181.8),
• Brain and other central nervous system (161.9, 95% CI 146.4 to 179.1),
• Thyroid and other endocrine gland (191.1, 95% CI 142.5 to 256.2), and
• Lymphatic and hematopoietic tissue (123.2, 95% CI 116.1 to 130.8).

The proportional cancer mortality ratio for cancer of the respiratory system was significantly reduced however (78.2, 95% CI 75.7 to 80.8, P<0.05))

Among female manufacturing workers, the significantly elevated proportional cancer mortality ratios (PCMRs) were:

• Kidney (PCMR 212, 95% CI 116 to 387), and
• Lymphatic and hematopoietic tissue (PCMR 162, 95% CI 121 to 218).

Computer manufacturing and semiconductor fabrication are known to expose workers to a variety of potentially carcinogenic chemicals, metals (especially arsenic, nickel and chromium), and electromagnetic fields (especially ultraviolet light, radiofrequency, and, in one process, x-ray radiation). Dr. Clapp noted that as manufacturing processes have changed over time in the industry exposures have changed as well.

Dr. Clapp received a consultancy by the plaintiffs' law firm to conduct the study but reported that the law firm played no other role in conducting the research.