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California teachers at higher risk for breast, endometrial and other cancers
Study of female educators also shows lower rates of lung and cervical cancers

UNION CITY, Calif., October 2, 2002 — California's teachers have significantly higher than expected rates of breast, endometrial, ovarian and several other cancers, according to researchers from the Northern California Cancer Center, the University of Southern California, the University of California at Irvine, and the California Department of Health Services.

A study of nearly 133,500 female teachers in California begun in 1995 shows that these 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, the investigators found. The research team's findings appear in the September issue of the medical journal Cancer Causes and Control.

"Clearly, teachers face a higher risk of many cancers. These women most likely have in common certain risk factors that contribute to their increased risk. As we gather more information on our study participants over the next few years, we should gain insight into the causes of these cancers," says Leslie Bernstein, Ph.D., professor of preventive medicine and chair in cancer research at the Keck School of Medicine of USC. Bernstein is the lead author of the study.

The study is the first to extensively examine cancer among schoolteachers. It reports on cancer incidence from 1995 to 1998 in 133,479 current and former public school teachers or administrators participating in the California State Teachers Retirement System.

Researchers expect that lessons learned about cancer within the group of participating teachers will increase understanding of the causes of cancer among all women.

"This is a very important study that will provide a huge amount of information on women's health issues now and in the future," says Dee West, Ph.D., chief scientific officer and executive director of the Northern California Cancer Center (NCCC).

About 87 percent of study participants are non-Hispanic white, though substantial numbers of African Americans, Hispanics, Asians and Pacific Islanders are involved.

Researchers found the following for teachers:

  • 28 percent greater risk of ovarian cancer
  • 59 percent greater risk of melanoma
  • 47 percent greater risk of lymphoma, mostly non-Hodgkin's lymphoma
  • 28 percent greater risk of leukemia, mostly chronic forms
  • 34 percent lower risk of lung cancer
  • 47 percent lower risk of cervical cancer
Investigators believe teachers tend to share certain lifestyle and environmental factors that may help protect them from cancer or increase their risk.

They found these characteristics among participating teachers and compared them to similar women throughout California:

They found these characteristics among participating teachers and compared them to similar women throughout California:

  Teachers California women
Average age at first menstruation 12.5 years 12.9 years
Never pregnant 21 percent 14 percent
Average age at first pregnancy 26.4 years 23.7 years
Average number of live births 2.3 2.7
Has had a hysterectomy 24 percent 29 percent
Body mass index less than 25 61 percent 53 percent
Has never smoked cigarettes 67 percent 55 percent

One factor that increases breast cancer risk in teachers is alcohol consumption. "It's important to note, however, that the increased risk for breast cancer was for women consuming two or more glasses of an alcoholic beverage a day. Consuming one glass a day, which research has found is good for a woman's heart, does not increase the risk of breast cancer," says Pamela Horn-Ross, Ph.D., senior research scientist at NCCC and lead author of a previous report from the study that appeared in Cancer Causes and Control earlier this year.

No one knows exactly why, but women with more education and income are at higher risk for breast cancer. This is at least partly because women who delay having their first child and have fewer children — until after college or starting a career, for example — are at increased risk.

Breast, ovarian and endometrial cancers share some of these reproductive risk factors. Teachers in the study tended to have their first baby later and had fewer children in total. Teachers also had high rates of use of hormone replacement therapy, which may be linked to breast cancer. These factors, however, do not appear to entirely explain the excess risk.

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. Smoking was low among teachers, which might explain the reduced lung cancer incidence among them.

In the coming years, the investigators will continue to follow the women in the study and look at family history, diet and environment. Horn-Ross, for one, will examine relationships between dietary patterns — including isoflavones, the phytoestrogens that are present in soy — and the risk of breast, endometrial and other cancers.

Teachers have long been suspected to be at high risk for breast cancer. The study grew out of reports of excess incidence of breast and other cancers among women in California school systems.

Although no one can prevent cancers from occurring in the population, people can take steps to lower their risks. General recommendations include avoiding smoking, eating a healthy diet and exercising. More information on cancer risk reduction is available from the National Cancer Institute's Cancer Information Service (1-800-4-CANCER), which in California is operated by the NCCC.

The study was supported by the California Breast Cancer Act of 1993 (tobacco tax), the California Department of Health Services and the National Cancer Institute.

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Leslie Bernstein, Mark Allen, Hoda Anton-Culver, Dennis Deapen, Pamela L. Horn-Ross, David Peel, Richard Pinder, Peggy Reynolds, Jane Sullivan-Halley, Dee West, William Wright, Al Ziogas and Ronald K. Ross, "High breast cancer incidence rates among California teachers: results from the California Teachers Study (United States)." Cancer Causes and Control. September 2002, Vol. 13, No. 7.

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2002 Northern California Cancer Center, NCCC Web Team



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