Affluence and Breast Cancer.

Abstract

High income, high socioeconomic status, and affluence increase breast cancer incidence. Socioeconomic status in USA breast cancer studies has been assessed by block-group socioeconomic measures. A block group is a portion of a census tract with boundaries that segregate, as far as possible, socioeconomic groups. In this study, we used US Census income data instead of block groups to gauge socioeconomic status of breast cancer patients in relationship with incidence, prognostic markers, and survival. US state breast cancer incidence and mortality data are from the U.S. Cancer Statistics Working Group, United States Cancer Statistics: 1999-2011. Three-Year-Average Median Household Income by State, 2010 to 2012, is from the U.S. Census Bureau, Current Population Survey, 2011 to 2013 Annual Social and Economic Supplements. County incomes are from the 2005-2009 American Community Survey of the U.S. Census Bureau. The American Community Survey is an ongoing statistical survey that samples a small percentage of the population yearly. Its purpose is to provide communities the information they need to plan investments and services. Breast cancer county incidence and survival data are from the National Cancer Institute's Surveillance, Epidemiology and End Results Program (SEER) data base. We analyzed SEER data from 198 counties in California, Connecticut, Georgia, Hawaii, Iowa, New Mexico, Utah, and Washington. SEER uses the Collaborative Stage (CS) Data Collection System. We have retained the SEER CS variables. There was a significant relationship of income with breast cancer incidence in 50 USA states and the District of Columbia in White women (r = 0.623, p < 0.001). There was a significant relationship between node involvement and income in Whites in 198 USA counties. Income was significantly correlated with 5-year relative survival in Whites with localized breast cancer. Income was not correlated with 5-year survival of Black race (p = 0.364) or other races (p = 0.624). The multivariate general linear model with income as covariate, 5-year survival by race as a dependent variable, showed a significant effect of income and White race on 5-year survival (p < 0.001), unrelated to Black race (p = 0.780) or other races (p = 0.618). In men, we found a nonsignificant positive correlation between county breast cancer incidence and income (r = 0.098, p = 0.168). Breast cancer risk factors, such as delayed childbirth, less breast-feeding, and use of hormone supplements, are more common in affluent women. Affluent women are more likely to have mammograms, which detect many cancers that might not otherwise be diagnosed. In addition, women in certain affluent ethnic groups-Ashkenazi Jews, Icelanders and the Dutch-are more likely to carry genetic mutations known to predispose to breast cancer. We hypothesize that women with more income can afford better cancer care and survive longer than poorer women. But our hypothesis does not explain why this effect should be limited to White women; or why node involvement increased with income in White women but not in Blacks or Hispanics. Further studies may be worthwhile.