UCSF

The purpose of this study was to examine the relationship between socio-economic status and established breast cancer risk factors related to endogenous and exogenous hormone exposures. This secondary analysis was based on a subset of data from a large epidemiological study of breast cancer, the Marin Women's Study, in Marin County California. Participants in the Marin Women's Study completed a 20 page self-administered questionnaire. Marin County California is an area with historically higher incidence of breast cancer. Previous efforts to explain the higher rates of breast cancer focused on the region's higher levels of socio-economic status. In a sample of 1,848 respondents, the following variables were examined in relation to education and income levels: age at menarche, age at menopause, total number of years menstruating, age at first pregnancy, number of pregnancies, total cumulative number of months breastfeeding, total number of years of oral contraceptive use, use of fertility medications, and the use of estrogen plus progestin hormone replacement therapy for greater than 5 years. Frequency distributions were calculated for each variable and median values were determined. The median education level obtained by participants was a Bachelor's Degree (34.8%). The median income level range was $150,000 to $299,999 (17.5%). Kendall's Tau-B and Cramer's V calculations showed the degree of correlation between education and income and the hormonal variables. The most significant associations between education, income, and endogenous hormones were not very strong. The greatest correlation was a later age at first birth and increased levels of education (Tau-B = 0.238, p <0.001), as well as increased levels of income (Tau-B = 0.159, p <0.001). There were almost no associations of significance between education, income, and exogenous hormone exposure. The results from this study show that an increase in breast cancer rates in Marin County cannot be explained by an association between higher socio-economic status with higher levels of hormonal risk factors for the disease.