Leukemia Incidence Among Workers in the Boot and Shoe Manufacturing Industry, Town of Union, Broome County, NY
Previous studies have shown a higher than expected number of people diagnosed with leukemia in Broome County, particularly in the Town of Union. When data from the study, "Cancer Occurrence by Common Drinking Water Source, Broome County, NY 1981-1990," were analyzed by age group, many of those diagnosed with leukemia were men aged 65 and older. In addition, Endicott Johnson (EJ), a shoe and boot manufacturer and major employer in the Town of Union had employed many of these men. Workplace studies have shown a link between leukemia and employment in the shoe and boot manufacturing industry. In response, the New York State Department of Health (NYSDOH) conducted a study to investigate the possible association between leukemia incidence among men aged 65 and older in the town of Union and employment at Endicott Johnson.
NYSDOH researchers conducted a case-control study to try to determine if those diagnosed with leukemia were more likely to have worked at Endicott Johnson than those without leukemia were. Those diagnosed with leukemia are referred to as "cases" and those without are referred to as "controls."
Case definition: Researchers used information from the New York State Cancer Registry to select cases composed of males aged 65 and older living in the Town of Union who were diagnosed with leukemia between 1981 and 1990. Thirty-six men fit these criteria. Researchers noted that 12 of the 36 men had been diagnosed with acute myeloid leukemia (AML), which has been associated with exposure to benzene, a chemical used in the shoe and boot industry.
Researchers reviewed death certificates for men aged 65 and older who lived in the Town of Union at the time of their death. For each case, four men were chosen to serve as controls. These men were about the same age and died at about the same time as the men identified from the Cancer Registry. However, leukemia was not listed on their death certificates as the cause of death or as a contributing cause of death. This process of finding people who have similar characteristics is called "matching."
Information about study subjects' employment was also taken from death certificates. Endicott Johnson employed about 29% of the study subjects (cases and controls).
Overall, the men whose death certificates indicated that they had worked at Endicott Johnson had a higher risk of developing leukemia than those who did not. In addition, the risk of AML was slightly higher among former EJ workers. One way to determine whether these higher risks are significant is to conduct statistical tests. When researchers performed these tests, the elevated risks were not statistically significant. However, this does not mean that there is not an association between leukemia and employment at EJ; it means that the tests were unable to show a statistical association.
As with any study, some factors that cannot be controlled make it difficult to draw clear conclusions. Four important limitations made it less likely that this study could show a statistical association.
- The sample size was small, and leukemia is a relatively rare disease. A good study design must focus on a specific area and specific time frame, which limits the number of cases.
- Information about work history was limited. The industry listed on the death certificate may not have been accurate, especially for workers who changed jobs late in life. Although most people probably worked at EJ for a long period, it is not known when they worked there or for how long.
- Determining work-related exposures involved some assumptions. Information about specific jobs was limited or missing on death certificates. Anyone who worked for Endicott Johnson was considered "exposed." However, given the large variety of jobs within the EJ factories, the levels of exposure to benzene, for example, might have been very different for each worker. In addition, it is not known if benzene or any other leukemia-causing chemical was ever used at EJ. Therefore, the lack of an association between leukemia and employment at EJ may mean that there was no exposure to these chemicals, or it may mean that not enough is known about who was highly exposed.
- Other factors may have had an impact as well. Since the development of leukemia ranges from two to 20 years after exposure, it is possible that many people developed the disease before the study period began. With the EJ workforce declining since the mid-1950s, both cases and controls may have retired and moved out of the area.
The results suggest an association between leukemia and working at EJ. This is consistent with other studies that investigated leukemia and employment in the boot and shoe manufacturing industry. However, this study does not provide enough evidence to rule out the possibility that the results were due to chance. Better information about the factors listed above would strengthen future studies. It would not make sense to study a more recent group of workers though, since many of the cancer-causing chemicals have not been used for several decades. In addition, there is no current exposure, since Endicott Johnson no longer manufactures shoes and boots in the area.
A copy of the full Leukaemia incidence among workers in the shoe and boot manufacturing industry: a case-control study is available on-line.
If you have any questions or would like more information about this study, please contact:
NYS Department of Health
Center for Environmental Health Outreach & Education Group
NYS Department of Health
Center for Environmental Health Bureau of Environmental & Occupational Epidemiology