Although black patients with colon cancer received significantly less treatment than white patients, particularly for late stage disease, much of the overall survival disparity between black and white patients was explained by tumor presentation at diagnosis rather than treatment differences, according to an analysis of SEER data.
Among demographically matched black and white patients, the 5-year survival difference was 8.3% (P less than .0001). Presentation match reduced the difference to 5.0% (P less than .0001), which accounted for 39.8% of the overall disparity. Additional matching by treatment reduced the difference only slightly to 4.9% (P less than .0001), which accounted for 1.2% of the overall disparity. Black patients had lower rates for most treatments, including surgery, than presentation-matched white patients (88.5% vs. 91.4%), and these differences were most pronounced at advanced stages. For example, significant differences between black and white patients in the use of chemotherapy was observed for stage III (53.1% vs. 64.2%; P less than .0001) and stage IV (56.1% vs. 63.3%; P = .001).
“Our results indicate that tumor presentation, including tumor stage, is indeed one of the most important factors contributing to the racial disparity in colon cancer survival. We observed that, after controlling for demographic factors, black patients in comparison with white patients had a significantly higher proportion of stage IV and lower proportions of stages I and II disease. Adequately matching on tumor presentation variables (e.g., stage, grade, size, and comorbidity) significantly reduced survival disparities,” wrote Dr. Yinzhi Lai of the Department of Medical Oncology at Sidney Kimmel Cancer Center, Philadelphia, and colleagues (Gastroenterology. 2016 Apr 4. doi: 10.1053/j.gastro.2016.01.030).
Treatment differences in advanced-stage patients, compared with early-stage patients, explained a higher proportion of the demographic-matched survival disparity. For example, in stage II patients, treatment match resulted in modest reductions in 2-, 3-, and 5-year survival rate disparities (2.7%-2.8%, 4.1%-3.6%, and 4.6%-4.0%, respectively); by contrast, in stage III patients, treatment match resulted in more substantial reductions in 2-, 3-, and 5-year survival rate disparities (4.5%-2.2%, 3.1%-2.0%, and 4.3%-2.8%, respectively). A similar effect was observed in patients with stage IV disease. The results suggest that, “to control survival disparity, more efforts may need to be tailored to minimize treatment disparities (especially chemotherapy use) in patients with advanced-stage disease,” the investigators wrote.
The retrospective data analysis used patient information from 68,141 patients (6,190 black, 61,951 white) aged 66 years and older with colon cancer identified from the National Cancer Institute SEER-Medicare database. Using a novel minimum distance matching strategy, investigators drew from the pool of white patients to match three distinct comparison cohorts to the same 6,190 black patients. Close matches between black and white patients bypassed the need for model-based analysis.
The primary matching analysis was limited by the inability to control for substantial differences in socioeconomic status, marital status, and urban/rural residence. A subcohort analysis of 2,000 matched black and white patients showed that when socioeconomic status was added to the demographic match, survival differences were reduced, indicating the important role of socioeconomic status on racial survival disparities.
Significantly better survival was observed in all patients who were diagnosed in 2004 or later, the year the Food and Drug Administration approved the important chemotherapy medicines oxaliplatin and bevacizumab. Separating the cohorts into those who were diagnosed before and after 2004 revealed that the racial survival disparity was lower in the more recent group, indicating a favorable impact of oxaliplatin and/or bevacizumab in reducing the survival disparity.