Lifetime passive smoke exposure and breast cancer in the CTS
Initial Award Abstract
Despite considerable research, the role of tobacco exposures in causing breast cancer remains unclear. Recently, evidence has emerged suggesting that active smoking may increase the risk of breast cancer but only when experienced during certain windows of vulnerability such as during adolescence or prior to a first pregnancy. An evaluation of such windows of vulnerability with respect to passive smoke exposure (i.e., exposure to the cigarette smoke of others) has generally not been possible due to the unavailability of detailed lifetime passive smoke exposure data. Also, most research conducted to date has focused on exposures in the home and has not taken into account passive smoke exposures in the workplace or other settings.
This project is designed to study the relationship between breast cancer risk and exposures to passive smoke in the California Teachers Study (CTS) cohort, a large well-defined cohort of female professional school employees who have an extraordinarily low rate of active smoking (5%) and have provided lifetime measures of passive smoke exposures. The objectives of this study are:
1. To evaluate the relationship between lifetime cumulative passive smoke exposures in various settings and breast cancer incidence. Settings to be considered include:
c. Social/other settings
d. All settings combined
2. To evaluate the relationship between time-period specific passive smoke exposures and breast cancer incidence. Time periods of interest will include:
a. Exposed in childhood only
b. Exposed in adulthood only
c. Exposed in both childhood and adulthood
d. Exposed prior to a first pregnancy (among parous women)
3. To evaluate whether these effects differ depending on a woman’s menopausal status or if she has a family history of breast cancer.
The study population will consist of the approximately 66,000 members of the California Teachers Study cohort who have never smoked, lived in California in 1995 (at the beginning of the study), and provided information on passive smoke exposures. Prospective cases of invasive breast cancer will be identified through linkage with the California Cancer Registry (CCR) data 1995-2002. Exposure data, including highly detailed information on passive smoke exposures (including timing, setting, dose and duration) will be obtained through a questionnaire mailed to cohort members in 1997. Information on other breast cancer risk factors will be gathered from the baseline questionnaire administered in 1995. The risk of breast cancer associated with the various exposure metrics of interest will be evaluated using statistical models, taking into account other known breast cancer risk factors. Elucidation of the role that tobacco smoke may play in the development of breast cancer may help us understand the biologic mechanisms underpinning this disease and potentially offer clues to breast cancer prevention and treatment. Research has suggested that women fear breast cancer more than other smoking-related diseases which actually carry a higher threat of mortality. If tobacco smoke exposure is found to be linked to breast cancer risk, it may serve as an especially motivating factor in reducing the use of tobacco and its accompanying host of related adverse health outcomes. |