Adjuvant Chemotherapy for Stage II Right-Sided and Left-Sided Colon Cancer: Analysis of SEER-Medicare Data
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Survival benefit from adjuvant chemotherapy is established for stage III colon cancer; however, uncertainty exists for stage II patients. Tumor heterogeneity, specifically microsatellite instability (MSI), which is more common in right-sided cancers, may be the reason for this observation. We examined the relationship between adjuvant chemotherapy and overall 5-year mortality for stage II colon cancer by location (right- vs left-side) as a surrogate for MSI.
Using Surveillance, Epidemiology, and End Results (SEER)-Medicare data, we identified Medicare beneficiaries from 1992 to 2005 with AJCC stage II (n = 23,578) and III (n = 17,148) primary adenocarcinoma of the colon who underwent surgery for curative intent. Overall 5-year mortality was examined with Kaplan–Meier survival analysis and Cox proportional hazards regression with propensity score weighting.
It was found that 18 % of stage II patients (n = 2941) with right-sided cancer and 22 % (n = 1693) with left-sided cancer received adjuvant chemotherapy. After adjustment, overall 5-year survival benefit from chemotherapy was observed only for stage III patients (right-sided: hazard ratio [HR], 0.64; 95 % CI, 0.59–0.68; p < .001 and left-sided: HR, 0.61; 95 % CI, 0.56–0.68; p < .001). No survival benefit was observed for stage II patients with either right-sided (HR, 0.97; 95 % CI, 0.87–1.09; p = .64) or left-sided cancer (HR, 0.97; 95 % CI, 0.84–1.12; p = .68).
Among Medicare patients with stage II colon cancer, a substantial number receive adjuvant chemotherapy. Adjuvant chemotherapy did not improve overall 5-year survival for either right- or left-sided colon cancers. Our results reinforce existing guidelines and should be considered in treatment algorithms for older adults with stage II colon cancer.
KeywordsAdjuvant Chemotherapy Propensity Score Propensity Score Weighting Colon Cancer Location
The authors thank Research Specialist Lauren Weeth-Feinstein, MPH, for her assistance in formatting and proofing this manuscript. This project also received funding from the University of Wisconsin Carbone Cancer Center (UWCCC) Support Grant from the National Cancer Institute, Grant No. P30 CA014520. This project was also supported by the Health Innovation Program, the UW School of Medicine and Public Health from The Wisconsin Partnership Program, and the Community‐Academic Partnerships core of the University of Wisconsin Institute for Clinical and Translational Research (UW ICTR) through the National Center for Advancing Translational Sciences (NCATS), Grant UL1TR000427. The ideas and opinions expressed herein are those of the author(s) and endorsement by the State of California, Department of Public Health the National Cancer Institute, the National Institutes of Health, and the Centers for Disease Control and Prevention, or their Contractors and Subcontractors is not intended nor should be inferred. This study used the linked SEER-Medicare database. The interpretation and reporting of these data are the sole responsibility of the authors. The collection of the California cancer incidence data used in this study was supported by the California Department of Public Health as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885; the National Cancer Institute’s Surveillance, Epidemiology, and End Results Program under contract N01-PC-35136 awarded to the Northern California Cancer Center, contract N01-PC-35139 awarded to the University of Southern California, and contract N02-PC-15105 awarded to the Public Health Institute; and the Centers for Disease Control and Prevention’s National Program of Cancer Registries, under agreement No. U55/CCR921930-02 awarded to the Public Health Institute. The authors acknowledge the efforts of the Applied Research Program, NCI; the Office of Research, Development and Information, CMS; Information Management Services (IMS), Inc.; and the Surveillance, Epidemiology, and End Results (SEER) Program tumor registries in the creation of the SEER-Medicare database.
Dr. Weiss was supported by the Agency for Healthcare Research and Quality (AHRQ)/National Research Service Award (NRSA) T-32 Institutional Training Program Grant No. 5-T32-HS00083.
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