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Authors Weiss JM, Schumacher J, Allen GO, Neuman H, Lange EO, Loconte NK, Greenberg CC, Smith MA
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Journal Ann. Surg. Oncol. Volume: 21 Issue: 6 Pages: 1781-91
Publish Date 2014 Jun
PubMed ID 24643898
PMC ID 4016118

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.

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