Abstract B56: Racial disparities in the receipt of adjuvant chemotherapy among stage III colon cancer patients
Authors: Murphy Caitlin C. , Harlan Linda C. , Warren Joan L. , Geiger Ann M. 
Published: October 2015

Background: Although the incidence and mortality of colorectal cancer (CRC) in the U.S. has declined over the past two decades, CRC disproportionately affects blacks, who have higher incidence and mortality compared with whites. CRC disparities are partly attributable to differences in risk factors, screening and early detection, and tumor biology; however, variations in treatment may also contribute to mortality differentials. Few studies have evaluated how disparities in CRC treatment have changed over time and across different settings. Using the National Cancer Institute's (NCI) Patterns of Care studies, we examined patterns in the use of adjuvant chemotherapy and differences for non-Hispanic whites and blacks in a population-based sample of stage III colon cancer patients during the period 1990-2010.

Methods: Patients diagnosed with stage III colon cancer were randomly sampled from the Surveillance, Epidemiology, and End Results (SEER) program in 1990-91, 1995, 2000, 2005, and 2010. There was oversampling by race in 1995, 2000, 2005, and 2010. Patients were categorized as non-Hispanic white (n=869) or black (n=385). Treatment data were obtained from medical record review with physician verification. All patients in these analyses underwent cancer-directed surgery. Patients who received or were recommended any chemotherapy agents as part of primary therapy were considered to have received chemotherapy. Log-binomial regression models with stratum-specific sample weights were used to estimate the association between race and receipt of adjuvant chemotherapy. Potential confounders included age at diagnosis, sex, insurance, comorbidity, and year of diagnosis. Effect measure modification by insurance was assessed using single referent models.

Results: There were few differences in sociodemographic characteristics among whites and blacks in the total study population (n=1,254). A similar proportion of white and black patients had high-risk features (e.g., poorly differentiated histology, bowel obstruction, positive surgical margins). Receipt of adjuvant chemotherapy increased among both white and black patients from 1990/91 (white: 57%, black: 45%) to 2005 (white: 72%, black: 71%) and decreased in 2010 (white: 65%, black: 53%). There were marked racial disparities in receipt of adjuvant chemotherapy in 1990/91 and again in 2010. After adjusting for potential confounders, black patients were less likely to receive adjuvant chemotherapy compared to whites (RR 0.82, 95% CI [0.73, 0.93]). A similar trend was observed when the analysis was limited to “healthy” patients age &lt;75 years and with a comorbidity score of one or less (RR 0.84, 95% CI [0.75, 0.95]). There was no difference in the types of chemotherapy agents or regimens received by race among chemotherapy-treated patients. Single referent models suggested the association of black race with receipt of adjuvant chemotherapy did not differ across insurance categories (private: RR 0.81, 95% CI [0.77, 0.94]; Medicare: RR 0.80, 95% CI [0.59, 1.09]; Medicaid: RR 0.85, 95% CI [0.69, 1.05]), although a larger proportion of black patients had Medicaid in all years of the study compared to whites.

Conclusions: The gap in the proportion of white and black stage III colon cancer patients who received adjuvant chemotherapy narrowed after 1990/91, but our findings suggest the disparity reemerged in 2010. The disparity persisted after adjusting for multiple confounders and across insurance types. Recent decreases in chemotherapy use may be due, in part, to the economic downturn and a shift toward greater use of Medicaid coverage. This shift followed the 2008 financial crisis, which may have also resulted in barriers to treatment access. Receipt of chemotherapy decreased more substantially in black patients compared to whites in 2010. Programs to address this treatment disparity are needed to improve quality of care, increase survival, and reduce disparities related to CRC mortality.

Citation Format: Caitlin C. Murphy, Linda C. Harlan, Joan L. Warren, Ann M. Geiger. Racial disparities in the receipt of adjuvant chemotherapy among stage III colon cancer patients. [abstract]. In: Proceedings of the Seventh AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 9-12, 2014; San Antonio, TX. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2015;24(10 Suppl):Abstract nr B56.