Previous SEER (Surveillance, Epidemiology, and End Results)-Medicare analyses have shown no definitive survival benefit for adjuvant chemotherapy (AC) with fluoropyrimidines. Impact of oxaliplatin-containing regimens for elderly stage II patients in real-world setting is unknown. We explored the utilization and outcome of AC after the Food and Drug Administration (FDA) approval of oxaliplatin.
Patients with stage II colon cancer (2004-2011) who underwent resection were selected for this analysis. Medicare claims data were used to ascertain the administration of AC within 120 days after surgery. The primary endpoint of the analysis was overall survival. We used the Cox proportional hazards model to estimate the effect of AC while adjusting for clinical and sociodemographic variables available in SEER. To adjust for referral pattern, a source of selection bias, we conducted an instrumental variable analysis using the surgeon of record and health service area.
A total of 16,468 patients were identified and 12.1% received AC. AC recipients were significantly younger, more likely to be male, nonwhite, married, and had lower comorbidity index. Their tumors had a more advanced stage, more likely to be left sided, and were less differentiated. The hazard ratio (HR) from the Cox model showed a statistically significant survival advantage for AC (HR=0.847, 95% confidence interval: 0.782-0.916). However, results from the instrumental variable analysis indicated that there was no definitive benefit of survival in AC recipients (HR=1.779, 95% confidence interval: 0.927-3.415). AC use decreased over time.
After controlling for referral patterns, administration of AC provided no definitive survival benefit. Future studies may elucidate the elderly population who may benefit from AC.