Calculating Risks
Female teachers in California are at higher risk for breast and other cancers
California's teachers have significantly higher-than-expected rates of breast, endometrial, ovarian and several other cancers, according to USC researchers and colleagues. They published their findings in the September 2002 issue of Cancer Causes and Control.
Their study of nearly 133,500 current and former public school
teachers and administrators participating in the California State
Teachers Retirement System during the late 1990s showed that
female educators experienced a 51 percent higher rate of breast
cancer than comparable California women. They also had a 72 percent
greater risk of endometrial cancer, according to investigators
from the Keck School of Medicine of USC, UC Irvine, the Northern
California Cancer Center and the State Department of Health Services.
"These women most likely have in common certain risk factors
that contribute to their increased risk," says Leslie Bernstein,
Ph.D., professor of preventive medicine and AFLAC Chair in Cancer
Research at the Keck School, who was lead author of the study.
This study, which grew out of reports of excess incidence of
breast and other cancers among women in California school systems,
was supported by the California Breast Cancer Act of 1993 (tobacco
tax), the California Department of Health Services and the National
Cancer Institute.
"Over the next few years, we will use the information provided
by teachers to try to better understand the causes of certain
cancers and other health conditions among women," says Dennis
Deapen, Dr.P.H., professor of clinical preventive medicine at
the Keck School and director of the Los Angeles County Cancer
Surveillance Program.
Researchers found the following for teachers:
o 28 percent greater risk of ovarian cancer
o 59 percent greater risk of melanoma
o 47 percent greater risk of lymphoma-mostly
non-Hodgkin's lymphoma
o 28 percent greater risk of leukemia
o 34 percent lower risk of lung cancer
o 47 percent lower risk of cervical cancer
"What surprised me about these results was the magnitude of the excess risk," says Ronald K. Ross, M.D., professor and Flora L. Thornton Chair in Preventive Medicine at the Keck School. "There are serious issues here that need to be understood and addressed."
Investigators believe teachers tend to share certain lifestyle
and environmental factors that may help protect them from cancer
or increase their risk. The researchers found these characteristics
among participating teachers and compared them to similar women
throughout California:
o Average age at first menstruation: teachers, 12.5 years; California:
women, 12.9 years
o Never pregnant: teachers, 21 percent; California women, 14
percent
o Average age at first pregnancy: teachers, 26.4 years; California
women, 23.7 years
o Average number of live births: teachers, 2.3; California women,
2.7
o Had a hysterectomy: teachers, 24 percent; California women,
29 percent
o Body mass index less than 25: teachers, 61 percent; California
women, 53 percent
o Never smoked cigarettes: teachers, 67 percent; California women,
55 percent
About 87 percent of study participants were non-Hispanic white,
though substantial numbers of African Americans, Hispanics, Asians
and Pacific Islanders were involved.
No one knows exactly why, but women with more education and income
seem to be at higher risk for breast cancer. This is partly because
women who delay having their first child-until after college
or starting a career, for example-and have fewer children are
at increased risk. Breast, ovarian and endometrial cancers share
some of these reproductive risk factors. These factors, however,
do not appear to entirely explain the excess risk, according
to Ross.
Meanwhile, cervical cancer, a disease occurring less frequently
among teachers, can be prevented through Pap testing-and a substantial
91 percent of participants reported having a Pap test sometime
within the previous two years. And smoking was low among teachers,
which might explain their reduced lung cancer incidence.
In coming years, the investigators will send out additional questionnaires
and look closely at factors such as family history, diet and
environment. Bernstein will examine relationships between physical
activity and breast, endometrial and ovarian cancer risk.
"We expect to see many more initiatives coming out of this
study," Bernstein says.
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