Traditional risk factor study (TRiFS): Preliminary report on risk factor prevalence and population attributable fraction estimates for breast cancer in Marin County, California

The objective of the Traditional Risk Factor Study (TRiFS) was to describe female breast cancer risk factor distributions in Marin County, California by using previously collected, individual-level data. The Marin County breast cancer risk factor distributions were compared with those of the other California counties and the State. Prevalence estimates for traditional breast cancer risk factors (e.g., age at menarche, family history, and age at first birth) were computed using data from the Marin County Breast Cancer Study of Adolescent Risk Factors (ARFS) and the California Health Interview Survey (CHIS). A reference set of relative risk values for the breast cancer risk factors of interest was assembled from published sources. Using the prevalence estimates along with these relative risk values, population attributable fractions were calculated for selected breast cancer risk factors and combinations of these factors. Approximately 84% of Marin County women were exposed to at least one of the following five breast cancer risk factors: earlier age at menarche, later age at 1st birth or nulliparity family history, later age at menopause, and/or higher postmenopausal body mass index (BMI). The results suggest that 50% of Marin County's breast cancer cases would be avoided if the traditional breast cancer risk factors considered in these analyses were eliminated. Later age at first birth and nulliparity after age 30 alone appear to account for about one-third of breast cancer cases in Marin County.