Abstract B48: Health care access and breast cancer aggressiveness contribute separately to racial/ethnic disparities in stage at diagnosis
Authors: Rauscher Garth H. , Campbell Richard T. , Weaver Kathryn , Warnecke Richard B. 
Published: June 2012

Introduction: Black and Hispanic women are more likely than their non-Hispanic White counterparts to be diagnosed at a later stage of breast cancer, which in turn contributes to both morbidity and mortality associated with the disease. We hypothesized that the stage disparity was due to differences in the rate of progression of breast cancer as well as differences in health care access/utilization, factors that might influence mode of detection (whether a cancer is detected through screening or through symptoms). The goal of these analyses was to estimate the relative contributions of health care access/utilization and breast cancer aggressiveness in explaining the stage disparity, using data from a population-based study of 989 recently diagnosed breast cancer patients (397 non-Hispanic White, 411 non-Hispanic Black, 181 Hispanic).

Methods: Stage at diagnosis was modeled as an ordinal variable using AJCC stage categories 0, 1, 2, and 3/4 combined. Analyses were done including and then excluding stage 0 (in-situ). A binary variable for mode of detection was defined to indicate symptomatic detection if the breast cancer was discovered initially through symptoms or clinical exam (i.e. not detected through screening mammography). Aggressive breast cancer was defined through higher histologic grade (three categories) and from a binary variable indicating if the tumor was negative for both estrogen and progesterone receptors. Reduced health care access/utilization was defined as lacking private health insurance of any kind, lacking a regular provider, and having less recent utilization of health care (mammogram, clinical breast exam, routine physical examination). In factor analyses, these five access/utilization variables loaded onto a single factor and were used to define a score with higher values indicating greater lack of access/utilization (Cronbach's alpha =0.65). We conducted path analyses of the aforementioned variables in M-Plus to estimate fully standardized indirect and direct effects between minority status and later stage at diagnosis. Mediation proportions were also estimated using the method of Karlson, Holm, and Breen (2010).

Results: The model was a good fit for the data based on chi square and other fit indices. After accounting for mediation, the direct effect of minority status on stage at diagnosis was not significant (p-value=0.31). Mode of detection was a strong mediator, accounting for more than half (mediation proportion = 59%) of the stage disparity. Breast cancer aggressiveness (31%) and Lack of access score (19%) each explained a significant proportion of the stage disparity, largely via their influence on mode of detection. When excluding in-situ breast cancer, breast cancer aggressiveness explained more (52%) of the stage disparity, while lack of access explained less (14%) of the disparity.

Conclusion: Black and Hispanic patients are more likely than Whites to be diagnosed with more aggressive tumor subtypes including higher grade and hormone receptor negative tumors. These aggressive tumors, in turn, are less likely to be detected on routine screening mammography, and more likely to arise as so-called “interval” cancers between scheduled screens. Simply equalizing access to timely, quality health care including high quality mammography screening, while important, will not eliminate the disparity in stage at diagnosis. Attempting to truly eliminate this disparity would require that available health care technologies and expertise be distributed in a manner that would take into account the disproportionate burden of aggressive breast cancer experienced by Black and Hispanic women.

Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):B48.