Geographic Variation in Oxaliplatin Chemotherapy and Survival in Patients With Colon Cancer.

Geographic disparity in colon cancer survival has received less attention, despite the fact that health care delivery varied across regions. To examine geographic variation in colon cancer survival and explore factors affecting this variation, including the use of oxaliplatin chemotherapy, we studied cases with resected stage-III colon cancer in 2004-2009, identified from the Surveillance, Epidemiology and End Results-Medicare linked database. Cox proportional hazard model was used to estimate the effect of oxaliplatin-containing chemotherapy on survival across regions. Propensity score adjustments were made to control for potential selection bias and confounding. Rural regions showed lowest 3-year survival, whereas big metro regions showed better 3-year survival rate than any other region (67.3% in rural regions vs. 69.5% in big metro regions). Hazard ratio for patients residing in metro region was comparable with those residing in big metro region (1.27, 95% confidence interval: 0.90-1.80). However, patients residing in urban area were exhibiting lower mortality than those in other regions, although not statistically significant. Patients who received oxaliplatin chemotherapy were 23% significantly less likely to die of cancer than those received 5-fluorouracil only chemotherapy (adjusted hazard ratio = 0.77, 95% confidence interval: 0.63-0.95). In conclusion, there were some differences in survival across geographic regions, which were not statistically significant after adjusting for sociodemographic, tumor, chemotherapy, and other treatment characteristics. Oxaliplatin chemotherapy was associated with improved survival outcomes compared with 5-fluorouracil only chemotherapy across regions. Further studies may evaluate other factors and newer chemotherapy regimens on mortality/survival of older patients.