Occupational Cancer Risk in California Teachers and Risk Modification by Medication Use
Doctor of Philosophy in Epidemiology
University of California, Irvine 2019
Professor Hoda Anton-Culver, Chair
Introduction: Teachers, as an occupational group, have been previously shown to have an elevated risk of breast, and endometrial cancers relative to the general population. However, no conclusive evidence regarding teacher-specific occupational risk factors driving this higher risk in cancer incidence have been established. Previous studies have found occupational physical activity levels to be inversely associated with risk of incident cancers, yet the conclusions regarding this association are not definitive.
The purpose of this dissertation is to assess cancer risk in participants of the California Teachers Study according to occupational characteristics and medication intake of school employees. The study will examine the association between various occupational characteristics and medication intakes among female school employees and cancer incidence of breast, endometrial, and malignant melanoma.
Methods: A prospective analysis of 133,479 female teachers and school administrators, aged 22-104 years, in the California Teachers Study cohort between 1995 and 2013 was conducted. Occupational characteristics and medication intakes were determined using participants’ responses to the comprehensive questionnaire administered at baseline. Age-standardized incidence rates were calculated according to participants’ occupational characteristics and compared to the incidence rates of California women, obtained from the California Cancer Registry. Multivariable Cox proportional hazard regression models were constructed to provide hazard ratios and corresponding 95% confidence intervals for estimates of cancer risk for breast, endometrial, and malignant melanoma according to occupational characteristics and medication intake of female teachers and school administrators.
Results: Throughout the eighteen years of follow-up in the California Teachers Study, there were 7,173, 1,351, and 1,919 teachers who developed breast cancer, endometrial cancer and malignant melanoma, respectively. There was an excess cancer incidence among California Teacher Study participants overall, and according to several occupational characteristics for breast, endometrial and malignant melanoma. Of note, lower levels of occupational physical activity was associated with an elevated risk across the three cancer types when compared to general female population of California and teachers with higher levels of occupational physical activity. Moreover, the elevated risk associated with minimal occupational physical activity levels was not mitigated by higher levels of recreational physical activity among participants of the study. Additionally, regular anti-inflammatory medication intake among study participants was associated with risk for breast cancer and malignant melanoma compared to non-regular users; there was no evidence for the difference in risk across the three cancer types according to statin use.
Conclusion: This study showed that female teachers and school administrators are at an elevated risk of breast cancer, endometrial cancer, and malignant melanoma which was largely driven by a lack of occupational physical activity and regular anti-inflammatory medication intake.