Abstract A49: Mediators of racial/ethnic disparities in radiation treatment among breast cancer patients.

Background: Radiation after surgery can reduce recurrence and breast cancer mortality yet there is some evidence that not all women receive guideline-concordant radiation treatment. Indeed, studies that have examined the receipt of radiation among women who underwent breast-conserving surgery have found that Black and Hispanic women were less likely than White women to complete their locoregional treatment. However, little is known about the factors that may facilitate or impede treatment. In order to better understand the causes of disparities in radiation treatment, this study seeks to: 1) determine the extent to which there is a racial/ethnic disparity in radiation treatment initiation, and 2) examine patient factors and hospital characteristics that may help explain the variation. Methods: Interview and medical record data came from a population-based study of 989 breast cancer patients (397 non-Hispanic White, 411 non-Hispanic Black, 181 Hispanic) diagnosed between 2005-2008. Of these, 87% (N=849) consented to medical record abstraction, including a linkage with the Illinois State Cancer Registry (ISCR). Patients who consented to the medical record abstraction and had single invasive primary tumors were considered for this study. Radiation treatment eligibility was defined according to the 2005-2007 National Comprehensive Cancer Network (NCCN) guidelines. The outcome variables included treatment recommendation, acceptance, and initiation which were derived from the interview, medical record, and ISCR data. Risk differences (RDs) were estimated using logistic regression (with marginal standardization). Potential mediators related to radiation initiation were identified, and then assessed by rescaling model coefficients using the method of Karlson, Holm, and Breen. All models were adjusted for age and time from diagnosis to interview. Results: Among patients with single invasive primary tumors (n=614), 443 patients (72%) were eligible for radiation treatment (RT) per the NCCN guidelines. Radiation treatment was recommended to 88% of eligible patients of which 93% accepted it. Among those who accepted treatment, 97% received radiation. This translated into an overall treatment initiation of 79%. Minority patients were less likely than non-Hispanic (nH) White patients to initiate radiation (0.75 vs. 0.85, RD=10%p=0.000). Minorities were more likely to have moderate-high grade tumors and symptomatically detected tumors which in turn were less likely to receive radiation (all p-values <0.01). Minority women were also more likely than nH White women (p<0.0001) to receive chemotherapy, which in turn was associated with lower receipt of RT (p<0.05). Together these factors explained 46% of the disparity (p=0.002). Conclusions: Patients who are eligible for radiation and have more aggressive appearing tumors at diagnosis are more likely to receive chemotherapy but at the expense of completing their locoregional (radiation) therapy. This disproportionately affects minority patients and results in underuse of radiation in these women. Greater diffusion of gene expression profiling (e.g. Oncotype) may improve cancer care not only by reducing overuse of chemotherapy but by eliminating chemotherapy as a potential barrier to receipt of RT. Citation Format: Abigail Silva, Garth H. Rauscher, Rao D. Ruta, Kent Hoskins. Mediators of racial/ethnic disparities in radiation treatment among breast cancer patients. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr A49.